While its true some properties have had lengthy cancellation policies, I think the OP's point that the general trend is for the timeline to creep up for leisure travel is equally true.

My thoughts to the OP the hotels (and possibly corporate wide) will continue to expand as long as the economy is doing well and they are seeing no ill effects from this policy change. As soon as occupancy rates dip you will probably also see the cancellation policy ease a bit but I don't think we'll ever see a wholesale change to 6pm day of arrival again (or something equally as generous).

Maybe they'll add an elite benefit like Hyatt that if the hotel policy is 48 hours, Titanium's get 24 hour cancellation (or something like that).