[easton]

I think the reason is that the Xbox 360 had a PowerPC chip/architecture vs the x86 of the current Xboxes, and the developers often wrote close to the metal optimizations that may not be feel good when put through a normal emulator (if they could even get it up to speed). This way, they know it'll work perfectly and can sell the game in the Xbox Store if you have never played it. (And can stop games that will never work, like Kinect games).