What's interesting is the 360 can definately support better AA and textures than that. As ever, this shouldn't be taken as confirming something about the HW so much as the software.
Assuming that is final build, then I see three options:
1 - due to space, even with three disks, SE dropped the resolution on the textures, etc. a bit and this is the result. Not horrible enough to affect the game IMHO but clearly not as nice as PS3. But again, this isn't down to the 360 but the textures themselves
2 - the late port engine on 360 just isn't as well tuned. SE has made comments they ended up with two versions of the engine, which is odd because ages back they said all their tools/engines were PC based and fully multi-platform. If the 360 version is a different cut of code then looking at the timeline for release it simply can't have had as much optimization and polish as the PS3 version. Again, nothing to do with the 360 simply SE having (in a reversal of Bayonetta) a weaker version of the engine on 360. The weak AA hints at some flaws around the engine.
3 - a combination of the above two, which is what I think personally. The assets look like they're simply weaker to squeeze it all onto the disks, as I guess SE had to juggle how much to compress the CG videos vs the actual game assets. The AA implies to me a not fully 360 optimized engine.
BTW if you can't see the difference (on the originals) then I'm a little amazed. There's no law saying everyone has to understand how to spot AA, texture resolution, etc. but on the other hand the entire image immediately isn't as sharp or vibrant on 360.
Anyway, I'll be waiting until I see 360 version (retail release code) content before accepting for sure these are final build images.
If it is I wonder why they didn't simply go for a fourth disk? 3 or 4, what's the big difference, and then they would have had far more space to play with an could have reduced the compression of the assets.
Try to be reasonable... its easier than you think...