What's in Wii is not a DVD drive. Sure it burrows DVD drive's OPU mechanism, but encoding/decoding is different, spins in a different direction, etc and Nintendo doesn't pay DVD royalty.
Blu-Ray drive hardware cost maybe reasonable, but the royalty is not. Thus just change the firmware of a "Blu-Ray" drive and blah, you have a proprietary "non-Blu-Ray" drive like Nintendo Wii U's drive and can skip on the royalty payment.
Microsoft is banned from offering one(Look at the Media Center Edition), only a 3rd party solution is possible.
But it doesn't matter, Microsoft has no intention of enabling Blu-Ray movie playback on any of its platforms and Microsoft's objective is to migrate everyone to streaming.
This requires two things.
1. Microsoft adding the Blu-Ray drive in Xbox 3 and paying the Blu-Ray drive royalty, big no no.
2. A 3rd party vendor selling a Blu-Ray player app for like $50.
Wii does not have a DVD drive. Wii's drive is modified enough to avoid DVD royalty payment(Ditto for the Wii U's drive), and Microsoft will go down the same path if it decides to stick an optical drive.