I find it terribly unreasonable to purchase a movie, and then be limited to using it on a single device. The tradeoff wouldn't feel worthy unless the purchase price was vastly lower than what they're trying to charge now.
It just bugs me to know that... at some point down the line, years perhaps, support for the PS3 will fall to the wayside, or the service will die, or you'll have a corrupt file that they won't fix... SOMETHING, that will make it so you won't be able to view the videos again. And then you've wasted your money.
If you buy physical discs, you can keep them in immaculate shape, and you'll be able to find a working DvD/blu-ray player for many decades down the road.