I heard that the reason to why the G25/G27 can't be used with the Xbox is Microsoft's fault
If this is true, they're supposed to deliberately limit the high-end (if not the entire) market of wheels to Fanatech. The limited market of wheels from other manufacturers would then boost Microsofts own market of wheels
I've heard that as well. Given MS's track record it would seem plausible. But according to some, it's way more complicated than that. Here's what Logitech's Chris Pate said over at their website when answering the same question:
Hello Xbox drivers,
While we understand many of our customers wish for us to make such a wheel, we are not licensed by Microsoft to manufacture force feedback wheels for Xbox 360 at this time.
-Chris
It would seem that in this case, the production of cross-platform wheels is being throttled by Corporate Lawyers and IP Licensing Fees. I'd be surprised if a big company like Logitech hasn't investigated cross-platform wheel functionality, but that's just speculation on my part.
I think the situation is clearly driven by legal and corporate wrangling because I've never gotten the vibe that it's too much of a technological challenge, and the existance of the Fanatec products seem to bare that out. There's no way Logitech would overlook the potential profits at stake when making a wheel that's compatible with the dominant console gaming platform.
It does seem odd that a boutique wheel manufacturer with limited production resources would be the only company capable of licensing and making a cross-platform wheel, doesn't it? I'll be there's an interesting story of corporate intrigue here, and perhaps someday we'll know "the rest of the story".