The argument over the "Only on Xbox" logo is funny. The exact same arguments have been going on since the release of the original Xbox. To my knowledge, in the seven years since the logo first came into use, no game with that logo has ever been released on a competing console. Countless such games have been released on the PC, but never on a competing console.
The closest thing to an exception would be Ninja Gaiden. Ninja Gaiden and Ninja Gaiden Black for Xbox both had the logo. Years later, Ninja Gaiden Sigma was released on the PS3. Technically Ninja Gaiden Sigma could be considered a different game, but it's pretty damn close. My bet is the exclusivity agreement only applied to the PS2 and GCN, not to future consoles.
Edit: Looks like there's several "Only on Xbox 360" games that have been ported to another console. Maybe the logo meant something during the Xbox era, but it doesn't seem to mean much anymore. I'm just curious: if Microsoft doesn't require a full exclusivity agreement for the logo, why don't they stamp it on all of their timed exclusives?
