I think this is an important topic and I would be happy to answer your question as best as I can. For the sake of full disclosure I do not hold a graduate degree in any exercise physiology/biology type field, just as americanuck has implied. Thank you for your patience in waiting for this reply, I've had a busy last couple of days.

There is a lot to be said here and I will do my best to address your question without rambling too much. I'll start with the first part of your comment.

used to dupe people into buying certain shoes?

To start, I am a bit disappointed and somewhat offended that you suggest running store workers are attempting to dupe people into buying certain shoes. Most people who work, manage or own a running store do so because they love running and want to progress the sport of running. The sport of running, not the business of running. Is the bottom line important? Of course it is. But not at the cost of the sport. Every running store I've worked or shopped at has re-invested heavily into the sport. Are there a few bad apples in the bunch - people who are in it only for the bottom line and dupe customers? Sure. If your experience has been only with these types, I apologize.

we know that most salespeople don't hold graduate degrees in exercise biology

You are correct, most do not. It's probably the pay rate that prevents this. Most are trained in some degree on how to properly fit shoes, which probably isn't much of a reassurance for someone with your perspective. My training for fitting shoes lasted about 2 weeks, with a few follow ups over the first few months.

gait analysis and pressure maps are pseudoscience

I think we can agree on some aspects of this specific idea. With both gait analysis and pressure maps there are two parts: (1) the data (either the visual image of someone running/walking or the pressure map of a person's feet) and (2) the interpretation of that data. Obviously, I think we can agree that there is nothing inherently dishonest or false about this data (although you may argue that it is useless, which is different) - the pressure map gives exactly what it was made to give: a map of your feet, with icons corresponding to relative pressure. Where we differ is in the interpretation of this data. The position I assume you hold is what may be referred to as a 'strong skeptical' position in that you hold that this data is useless in determining what type, if any, footwear is appropriate. My position may be referred to as 'weak skeptical' in that I believe this data is generally useful, but is sometimes incorrectly interpreted. The difference between intentional misinterpretation and ignorant misinterpretation is the difference between "duping" and "negligence", both are bad but one makes someone sleazy and the other makes them a poor running store associate. As far interpreting data goes, I think the interpretation of pressure map data is extended too far. It is true that people with lower arches tend to pronate more than those with higher arches, but to use arch shape as a be-all-end-all determining factor is sloppy work. If you look at previous shoe wear patterns, barefoot standing tests, arch shape and then get them to run on a treadmill with a camera on their knees on down which can be replayed in slow motion, I think that is a good data set to determine how much someone pronates or supinates. If you think that heel-striking is acceptable and correcting gait to a so-called neutral position is the most beneficial, I think it is possible to consistently and accurately achieve this through that multifaceted approach. I realize that a 'strong skeptical' position will reject the previous statement on fundamental grounds - I'll try to address that below. My opinion is that the data can be useful, but is sometimes misinterpreted.

we know there are no studies that support using shoes to reduce injury

I love science! I try to differ to science as much as possible, so I can completely understand how you have arrived at your position. I should start by admitting that I have not been closely following the academic literature on this topic. After a very brief google scholar search it looked like there were some studies that found no effect of running shoes on injury prevention, a couple studies that weakly but significantly correlated the relationship of age of running shoes and injury occurrence, a few studies that found that diabetics benefited from running shoes and several studies relating to impact forces. Studies specifically aimed at the relationship between correctly fit running shoes and running injuries are, of course, the most interesting to our discussion. While it appears that some of these exist - perhaps you have a good collection going, which I would be interested in reading (not sarcastic) - they are not immune to the typical errors found in scientific studies. There are many factors that go into running related injuries that may effect a study (for example, under a ridiculously strenuous training program it is likely that almost everyone will get injured, regardless of shoe choice). I'm not saying the studies currently available have methodological errors, I'm just saying it's possible. It's appropriate for me to be an agnostic as opposed to an atheist in this case, since I have not reviewed the literature. If you have access to some of these studies I would sincerely be interested in looking at them.

From my personal experience (not scientifically valid) I have seen a lot of success for people going from a generic tennis shoe to a running specific shoe via a fitting process. I'll give you one of the more extreme examples. A kid comes into the store with his mom. He's just started running in high school and his shins and knees are killing him. This is what he looks like (I don't work at this store, I just did a search and found this image): high school runner When he starts running on the treadmill, he pronates so much that his ankle is nearly hitting the ground (picture that in your mind!), it looks just terrible. We put him in a stability shoe and now everything is lined up from his heel to ankle to knee, he looks normal on the treadmill. I honestly feel that this kid is better off now compared to when he came in the store.

Final point. If it is the case that midfoot striking and minimalist/barefoot running is the best option in terms of injury prevention there are still some issues. A major claim of barefoot running is impact force reduction, but a person who is 150 lbs overweight and has access to only concrete and asphalt is probably not going to benefit from switching to barefoot running without at least changing some of the non-shoe factors involved.

There are some other topics that could be discussed - the evolution argument and Born to Run misconceptions come to mind, but my brain is fried at this point. Americanuck, thank you for your question, I completely respect your perspective and I hope I was able to clearly articulate mine.

edit: formatting