Thanks, if that turns out to be true (and i guess it is since there actually is a name behind that claim and its from R*, in contrast to some "unknown" developer) then this is the only official information about possible problems on the Xbox 360 version we have.
Plus it sounds very plausible to me (limitations because of optional HDD on the 360). Additionally, they might even have problems fitting it on a DVD9, not because of size, but because a DVD9 has much lower transfer speeds on the 360 drive and that could very well also be a limiting factor (when they would have to go for a DVD5 because of that) as well.