* In America, third-party support is essentially locked in; shooters, sandbox games, WRPGs, and other similarly "hardcore" genres do fuckawesome on X360, while casual games can, at least, sell like gangbusters on Wii. PS3 moves enough software that it's arguably leaving money on the table to do 360 exclusives; as with PS2/Xbox last gen, there's not much reason not to do either day-and-date or six-months-later ports of most Western-developed titles with an X360 lead SKU to PS3, though arguably in some cases the exclusivity will boost X360 platform sales enough to make up the lost PS3 sales. There's a strong indication against PS3 exclusives, however; nothing exclusive on the system has stuck effectively, even hyped 1st party titles.
* In Japan everything is a fucking mess. DS is the only platform that can be considered an unqualified success, hardware and software; third parties who make use of its strengths (Level 5, Square-Enix) are doing well. Every other platform is having software problems; 3rd party Wii software is (at least thus far) underperforming its hardware sales, PSP is a pit for anything that isn't an MGS/FF/KH level title, PS3 is performing poorly and X360 is a goddamn disaster. This leaves PS3 as the most viable HD platform, but obscures the fact that unlike America, Japan has demonstrated severe disinterest in HD gaming; inasmuch as Japanese developers are interested in pushing HD content (and they seem to be reasonably interested in it) PS3 is their best platform (except when they aim at American audiences, Capcom-style) but so far the economics simply don't support this strategy very well -- $10-20 million dollar titles selling <300k aren't a good investment.
* Europe is somewhere between at par between X360 and PS3 and a commanding PS3 lead, hardware-wise; its software sales seem to be even more slanted towards Nintendo than elsewhere in the world. As far as I can tell, there's no evidence on hand that PS3 is producing software sales that are either as actively excellent as X360's American software numbers, or as far ahead of X360's Euro sales as X360's American sales are ahead of PS3's American numbers (but please do correct me if there are unambiguous indicators that this is the case) -- it seems most likely that PS3 is putting up solid (but not necessarily remarkable) software sales, while X360 is somewhere in the range between solid and poor.
With that sort of worldwide picture, X360 comes out looking stronger in many cases: if you're an American developer, it's your unambiguous choice; if you're a Japanese developer (and you're making hardcore action games) your combined US+JPN sales are likely to be much higher on 360 than PS3; if you're a European developer, you might lean towards PS3, but it's unlikely to be the only obvious choice the way the 360 is in the US.
EDIT1: Because this generation sucks worse for third parties than the last one did; PS2 winning every territory and selling software well made decisions like this easy, while the current market is much less certain for anyone.
EDIT2: Holy fuck, that's a long post. :lol