Backward compatibility guarantees is a significant one, I think. A lot of the QA process for console games is predicated on testing against a fixed set of hardware configurations, and various race conditions and other weirdness can start crawling out of the woodwork even with modest changes. This has been seen on many games running on emulators, on hacked console firmwares that allow overclocking (e.g. by running the CPU at the "native" clock speed in backward compatibility mode), or with framerate unlocking patches.
