The code name for 10.2.7 was Smeagol. As PGant said, Jaguar fine tuned to work on the G5 (and most likely has a few enablers or something built in). 10.2.7 (the one on the G5s) won't run on any other computer however as far as I've heard.
I'm a little puzzled by suggestions that 10.2.7 won't run on non-G5 machines. Since these are the same machines that will run Panther, and Panther's specs go back as far as G3s, then it seems like a reasonable deduction that the next upgrade for 10.2 will serve all platforms.
Then again, this is all idle speculation on a Friday afternoon.