I prefer the MS approach, personally. It doesn't leave your older systems out in the cold, in a "yeah we're done, never gonna touch this again" way once the new systems come out, since they seem to do BC better than Sony has thus far. I also think that the current gen still has life left in it, so not pushing people to upgrade ASAP if they don't need to (especially with the current situation) is a wiser move.
I do think generations are a good idea, and if you're going to make a generational split that's fine too, but pushing people to buy your system for years and years then dropping it suddenly when it suits you (as the platform holder) isn't something I've been enamored with. I also do suspect that Sony would be more eager to make a switch to a new gen since they announced most of their big PS4 titles quite a while ago and have almost released all of them.