I've heard that Sony has an Indie program that allows you to retain rights to your IP. I'm not sure what their cut is? I'm sure it's comparable to XBLIG/XBLA/Steam. I can certainly see Sony as being "desperate". I honestly have no clue how well PSN is really faring these days compared to XBLA. My perception is that XBLA is dominating PSN.
[disclaimer: I am not (yet) a PSN or XBLA developer so I can only speak for what I've heard from fellow developers]
Sony has the Pub Fund : when development is finished, they may (not will!) pay you back development costs in the form of royalty advance with a 100% recoup rate. So it's a pretty big deal if you can get it, they basically ensure you that your game is profitable.
As for the royalty rate it's similar to Steam or XBLA i.e. in the region of 70% if you self-publish the game.
As for XBLA vs PSN : XBLA is a larger market, I'd say about 2 to 4 times bigger. I've heard some people estimate the XBLA market to 700 millions $ to 1 billions, but I don't have any data to back this up.
Most developers these days advise to chose PSN over XBLA, though, as Microsoft has apparently become really unsuportive of independent developers. I'd talk to both and see what happens.