I haven’t used the App Store (I don’t use OSX much, so haven’t updated beyond 10.5.6) but when it was announced there was this article on Engadget, with an overview of the App Store review guidelines.
6.3 Apps that do not use system provided items, such as buttons and icons, correctly and as described in the Apple Macintosh Human Interface Guidelines will be rejected.
I’m not sure if that’s saying apps will be rejected if they use system provided icons incorrectly, or if apps that don’t use system provided icons at all will be rejected.
If it’s the latter, then Blender probably won’t be able to make it into the Store.
But apart from that I’m all for it being in the App Store. I original discovered Blender while browsing the ‘Downloads’ section of the Apple website (which they’re now apparently taking down as the App Store replaces it) so can see that having it listed in the App Store could help draw in new users.