I think it is reasonable to expect that Leopard will ship late. Steve has gone on record in the past that unlike the first 4 major revisions of OS X, which rolled out quickly, future revisions will take more time and will not be as frequent.
It is likely to expect that Leopard will ship late based upon that logic alone. I mean full 64 bit support, ZFS file system, etc, while not sexy to Joe Consumer, is nothing to sneeze at. If they have secret "Sexy" features that know one has seen yet then it will be late.
As for AppleTV (Unknown_Error), A) it runs on a stripped down version of 10.4.7 not Leopard, and B) was delayed due to video card software issues with the built in NVidia card.
Yeah, Tiger WILL support G5's, but based on Apple's track record, it will probably be the last major release to fully support PowerPCs.
Intel is Apple's Mac future and they will invest most of their efforts in OS development in that direction. It is in the company's interest to drive future sales through hardware upgrades.
What If There Are No Top Secret Features in Leopard?
Leopard Preview Gives Clue to Top Secret New Feature