It's odd they still use combos. I just purchased a fantastic, fast SuperDrive for $25 3 months ago. The prices are so low, so hardware prices can't be much of an issue.
Its not really all that odd. They use the different drives to further differentiate their models of take for example, the MacBook.
The low end MacBook has slightly less of everything, and a combo drive to boot. As for the next MacBook up, its the same as the black MacBook except white. Its a way of encouraging you to spend 200$ more and get a few minor things. Differentiates products.
Personally, I think all their computers will all go super drive standard. But the MacBook Pro, The Mac Pro, and the iMac will have the option to go blue-ray. The lower end iMac's (the two cheapest models) will probably keep the super drive and have no buy to order option for blue-ray.
I think if they keep the prices of their computers the same, the ones able (MBP, Mac Pro, iMac) should have a blue-ray drive included in that price. If they drop their prices 200-300$ on everything, or so, they will have a option for one.
I really hope they do a price drop. Its needed... their hardware is way over priced. I also hope to god they give the MacBook one more USB port, and maybe the option to not have a optical drive (replace it with another hard drive etc) plus some flash card readers (is it SD readers?).
Just my two cents.
Cpt. Morgan