I think it's case by case - it makes sense that Japanese devs in general - and SEGA in this case specifically - would originally have favored a platform they expected to trump the 360 domestically. Capcom has bucked this trend, however, and has shown how an export-oriented model targeted towards 360's large install base can lead to great financial rewards. SEGA is on that game anyway though, and VF5 being exclusive previously was definitely the exception to their in-house rule.
We'll see what plays out with the other J-devs as time goes on.
I honestly was speaking more towards Western devs though, that I see very equal in their support of the consoles outside of 1st and 2nd parties, and even favoring 360 more often than not. Part of this is install base, part of this is tools, and part of this is the mania that is UE3 and its 360-firendliness (compared to PS3) until recently.
The J devs are obviously some of the most storied and important devs in the industry, but I don't think we can speak about devs in general when talking about their actions in particular, because they really do tend to be much more cautious in the way they approach things.
So, if we're speaking development at large, I think that it has favored the 360 to an extent, and if we're talking about Japanese devs, I agree that they defaulted to Sony at the beginning (with some exceptions), but that things are starting to shift towards increased 360 support.
By the way, I know absolutely zero about the graphical differences between the 360 and PS3 versions of VT3, so I'm not speaking to it; I imagine that they highlight 'the usual' subtle differences. In terms of online vs non-online play though, clearly MS' turnkey support for such has made a great different in this case, and is an example of the benefit that framework provides to their developers (and community). That SEGA hasn't been bothering with online at all for PS3 I will be honest and say I find disappointing.