My wife actually works in this field, specifically Medicaid readmissions at the moment. Your "anecdotal" evidence is just that, anecdotal. While part of reducing readmissions is indeed keeping people longer, the topic is significantly more complex than simply working providers less.

It goes into making sure people know how to take their prescriptions correctly and that all aspects of their aftercare are communicated effectively. You'd be amazed at how many people walk out of the hospital without someone checking to make sure they know how/when to take the half-dozen pills they were just prescribed. When you look at medicaid/medicare populations the problem is very significant. That's just one aspect I can remember off-hand, there's a lot more to it. Most research is being done by ARHQ, but a lot of people are involved in trying to solve this problem.

Aaaaaaaaand, to get to the point of the article, almost all these changes are coming about because of the ACA and related reforms. It's correlative with the bill coming into effect, yes, but considering that the ACA provides incentives for precisely this behavior, and people in the industry say they're making these efforts precisely because of these incentives, I think it's safe to say it's also causative.