I have been thinking about this topic for quite some time now. What is preventing Apple from officially supporting BD drives and HD content from them? Steve Jobs is on the Blu-Ray Steering Committee for Pete’s sake!
Not technology. With the latest refresh of the Mac Pro, even the base model has hardware support for decoding the HD content with ease. MacBooks and iMacs have been that way for a while as well.
Not encryption. The HDCP stack is now supported fully by all of the components.
Not licensing. iTunes/AppleTV already has access to a ton of HD content.
The only answer (that I can think of) is money. Playing HD content over DVI or HDMI requires royalty payments to the patent owners. My guess is that Steve is waiting for DisplayPort (the royalty-free VESA standard for HD connectivity) to become prevalent. He will then announce new video card options for the upgradeable Macs and new version of the MacBook to support this technology. At this point the drives will become suddenly available and viewing BD content on the Mac will only require a quick software update (which removes the blocks in place).
Oddly enough the catalyst for this will be Windows Vista. With the release of Service Pack 1, Microsoft will add support for UEFI (making more video cards compatible with Mac) and DisplayPort as well. This will drive changes in the video industry with new graphics cards and displays coming out in force later this year. Add HP throwing their weight in the UEFI arena and we can see a lot more options for the Mac in the near future.