I think the short answer is they can't.
If you think about it, apart from exclusive IP consoles are essentially interchangable. They are simply HW that plays a game.
Sure, you can try and use specifications - but those can always be matched.
You can be innovative (like Wii) but that can be copied next time out or added as an extra (I'm actually surprised both Sony and MS have been so slow to get out a bunch of simple motion control games, particularly Sony as they already have basic motion controls already).
And unless money (paid exclusives or studies) or other reasons are involved (company choice for simplifiation and focus such as Insomniac) there is little advantage right now to being exclusive as a developer.
I think AC, COD4 and DMC4 were the tipping point when I realised that PS3/360 could co-exist although each was limiting the others growth, as both easily sold enough of each system to be a success for both.
Now the standard way to be different is either different services or unique products.
But of course unless we're talking unique IP those can be copied. PSN for Live, for example, or BR player for 360, etc. That can take time of course, but it can be done.
Right now the only real difference between the two is a relatively small set of exclusive games and BR and brand recognition.
Try to be reasonable... its easier than you think...
