Ooooo, I love conspiracy theories…
http://news.com.com/2061-11516_3-6176049.html?tag=nefd.aof
What do you know that your not telling us Mac?
Most of the Mac OS X team was transfered to work on the iPhone (and AppleTV both run OS X) Leopard’s features will be finished on time in June (and will be demoed live on stage by Steve himself) but apple wants time to do bugfixes and to let developers beta test it. If they had not transfered the resources to the iPhone project there would have been time to to the beta phase before WWDC but it has been set back. Instead there will most likely be one more 10.4.x release before leopard comes in October.
FYI: Only the very high ups in Apple knew it was going to be delayed, all of us Retail guys are just as clueless as you are.