I'm pretty sure they're not talking exclusive content for PS3 AND PC. At least, I can't see Bethesda doing ANYTHING exclusive for PS3 given how much they take from Microsoft in marketing payments. With PC they can always write it off as "Oh, the hardware can't handle it," but with PS3 it's just unlikely. That said, I'd LOVE to see another fixer-upper for the PC version like grass shadows and the HD texture pack. Maybe official in-world (no loading) cities?
IDK, the PS3 can handle a lot more than the xbox. If done right I could see it being done.
The margin between consoles is insignificant. The CPU in the PS3 is better, but games are more bound by GPU (and the 360 GPU uses a more modern architecture). In addition, PS3 handles memory in a way that doesn't give devs the same amount of freedom. PC handles it the same way, but that's solved by having more memory in even a low end PC GPU than an an entire console. At the end of the day they're both boxes of hardware that was considered high end (read: not even the best you could buy) 6-7 years ago.