Not a good reason, but it's most likely that the Res Inns and TownePlaces are considered long stay hotels. Therefore, some folks may stay for 30 days or more at a time. My guess is that Marriott doesn't want to give these long time stayers the full allotment of points. Just a theory.
Absolutely they do. And some long stay properties don't credit you full nights. I stay at MEA all the time. I think they limit it to 30 nights per year credit regardless of how many you actually stay. Since I'm always Platinum I don't care about the nights so it doesn't bother me.