On Apple's sales site when you are on the page with the 3 options of the G5 to buy it says that the version on Jaguar is a "Specially Tuned" version.What's different?
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.
10.2.7 will run on older machines.. of course.. it is still a 3 bit OS with added support for the G5.. it will have a few different libraries and such but nothing significantly different.
To clarify what I said, it was that 10.2.7 was the only version of Jaguar that would have some special libraries and files for the G5 to run it. So in essense, 10.2.7 is 10.2.6 with G5 support.