Look at how the cases are arranged
In order to make the hard drive on a MacBook Pro as easily accessible as it is on the MacBook, Apple would have to move the DVD drive to the side of the computer as opposed to the front. There is no good way with the DVD drive in the front of the computer to have the drive pointing into the battery compartment rather than parallel with it. Because SATA involves a plug you have to pull the drive out directly away from the plug.
If they moved the DVD drive to the right side as with the MacBook, it allows for the drive to be reachable from the battery compartment, but that raises problems with where you put the ports. If MacBook Pro users are OK with all the ports on one side of the computer, or if they're OK with a redesigned display hinge and some of the ports on the back, than that's another matter. I'd actually be OK with the second option; I'd rather have the DVI port and a set of the less used ports on the back than on the right side, where they interfere with a dual monitor set-up. But even with this option, you've got the components arranged in an asymmetrical way inside the case which could lead to the same irritating left-sided heating you have in the MacBook.
But I'm not OK with having everything on the wrong side of the keyboard for a right hander, as with the MacBook.
And I think some people are going to want the DVD drive in front, especially on the 17, where people on a train or a plane would be ejecting DVDs into their neighbor's lap with a side-saddle arrangement.
If you have the DVD in front, it would take some creativity; either a long skinny battery to fit between the DVD and a hard drive mounted parallel with the front of the computer as in the MacBook, except in this case you'd have the drive and the battery forming an L shape, and it would only work in the 17 anyway as you would not have room in the 15 to slide the drive all the way out -- or a removable panel on the bottom of the computer through which to access the drive.