I point to my earlier post on page 1 of this thread. I agree with your reasoning, but I just can't see how Apple would be ready to preview 10.6/11.0 that soon after releasing Leopard.
If past practices by Apple is any gauge they could at the very least tell developers what's going to be in 10.6..
Tiger was released April 29th 2005 and then Apple announced the transition to Intel at the WWDC05 and said the next OS would be called Leopard.
I see no reason to think this won't happen this year.Apple has gone past the transition and can now concentrate more on the OS than they did earlier.