I found this post by MacPomme very interesting
https://forums.macrumors.com/showthread.php?p=3492356#post3492356
While he may be wrong, he makes some great points. Well worth reading.
As he says - Apple may have tied the new OS development into some new hardware developments (just as the iPhone ties software and hardware development together). If this was so, a demonstration of Leopard would stop people buying the old hardware.
Thanks for posting that, interesting read. There is definintely more to Leopard than we know.