Would depend on the features that were Gold exclusive. I don't think this would work very well for anyone involved. MS makes less money thus they'd surely invest less into XBLA exclusives, timed exclusive content. And most importantly, do they then charge for bandwidth? If so, no way does every XBLA game have a demo. And do they invest as much into their matchmaking system, which they provide to every developer on XBL that wants it? Probably not. So the result is you get a less quality online experience.
Who knows about sales. Do they do that Rockstar loan deal for GTA IV if Live isn't making them a lot of money? Or CoD 1 month exclusive DLC? Who knows how much these little things add up to in sales. I would guess there would be no huge difference in sales. Sony has free online play and pretty much never advertises it.







