Not that anyone will read this, but ...
Steve knows how simple accounting works. A 22% profit margin on a $1,000 computer is $220. That's a LOT of rental downloads. In other words, for this argument to make sense as the reason Apple isn't putting BluRay into their computers, you'd have to assume that every purchaser of their computers (on average) makes about 73.6 MORE $2.99 rentals over the course of the lifetime of that computer than they would with a Blu-Ray drive installed (again, a $2.99 rental of a hi-def stream is pretty competitive with a Blu-Ray disk rental and certainly less expensive than purchasing the disk for a single viewing).
I don't think Apple makes anywhere near that many HD rentals via iTunes. In fact, I'd be surprised if the HD rental business is even a non-negligible profit center for Apple. It's a stake in the ground, staking a claim on the future, not a reason for Apple to sabotage current profits to hold off the inevitable.
Personally, I completely agree that the old plastic disks are past their useful lifetimes. I'd much rather put 300 movies on a $100 terabyte drive than have to store 300 DVD jewel cases and disks, and I'd much rather be able to scan through that library of movies in a searchable and filterable interface on my 50" TV than leaf through the jewel case covers or read the sides of those jewel cases to find what I'm looking for. Even if the quality is lower (ATV quality instead of DVD quality, or ~DVD quality HD instead of BluRay quality), the convenience and durability of bits instead of disks is a huge benefit.
Would having a BluRay in my Mac lessen how often I rent from iTunes? Probably not. I like the convenience of renting from iTunes on occasion. Of course, it's really rare that I even do that, more often renting a disk from RedBox or the like to watch for the night, or if I like it a lot buying the DVD, ripping it to my media library, then putting the DVD in cold storage as disaster recovery ... maybe I'd switch to renting BluRay disks for the real visual movies, but that's eating into the DVD rentals a whole lot more than the iTunes rentals (which, really, again, compete with DVD rentals of quality, not BluRay, despite the "resolution" being 720p).