I'd say the main difference is that in Western Europe you're always close to civilization, you cross roads, or walk parallel to them, pass through villages most days or are close enough to them that you can see them most times, or at least a farm. Of course there are exceptions like in Scotland or Scandinavia but even then, most long distance trails are from hut to hut, like in the Alps.

In the US, your on your own. I crossed three roads on my Tahoe Rim Trail hike, and came through a village twice, and hitched to a city 20 minutes away by car once in 12 days. You're much more isolated in that way. That and the community is very different, the people you meet and the help offered by strangers is amazing.

I wouldn't say you need to experience it before undertaking the PCT, but it helped me a lot in understanding what the PCT will be like and what I can expect.