But since this is a massive undertaking, it has to be marketed towards a massive audience. And keep in mind, it won't span years on just the 360 and PS3; it is almost guaranteed to be cross-generational.
It might very well make more sense to bet on the current generation than the next in terms of traction and longevity.
It might appeal to people who don't plan on buying the next generation of consoles in particular, because it reinforces their belief that there isn't a need to get a new console here and now.
Technically you can just move an account up to the next version of the same console, but that still seems... strange.
They pretty much have to say "360 and PS3", because "next gen consoles" or "unknown platforms" would be a dead giveaway. I expect them to make another announcement next week amending this, after the official unveiling of Sony's new machine.
I don't really see anything wrong with this. I can't imagine it costs much to port from 360 to Infinity (and PS3 to PS4). They get a wider user-base, which is extremely important for an MMO, and many will buy the game twice when they eventually upgrade their consoles.
We'll see though :)