Combo drive justification:
for those who prefer to purchase an external DVD burner. I've got one, so I buy computers w/o Superdrive. I save on each CPU purchase, and I can upgrade my external at anytime and get the speed/DL/feature boost on all my machines, plus take the external to a family/friends computer if needed.
You can now 'burn' iDVD to a disk image (preferred method anyhow), so only the final step of burning the physical DVD requires a burner. A long time can pass between projects, plugging in a cable is no big deal, as far as I'm concerned.
It's an option that I actually prefer.
-KCMW