While I think Wombat had it right that Sony hit it out of the park in comparison with BF3, it's only because of name recognition, sadly that's the most important thing. When it comes to real comparisons I think Microsoft is the better deal and going to cost them more.
BF3 is on sale for $5 all the time now on pc, obviously more on console but EVERYONE already owns it that really wants it. Sure you may not own it on ps3 but if you have it on 360 or pc why would you want it for ps3? Smaller multiplayer communities and starting your unlocks all over from scratch again?
Defense Grid is a solid game and valued about the same as BF3 maybe more and no one has it, lots more will likely download it.
So Sony wins the PR front because of name recognition and it will likely cost them very little in comparison to Microsoft probably much larger expense to have everyone scoff at them for a relatively unknown game. It's a double win for Sony but unfortunate.