I think they made the right choice there.
If you've got eleventy zillion pixels on a 15" laptop screen, you really don't want to have to drag around a 17". If you do want more screen space, it's easy enough to plug in a 24"+ screen at a desk. (J's 13" MacBook Pro has a 24" screen, a mouse, and a keyboard attached to it.)
A couple of years ago a guy visited at work and dragged out his 17" MacBook Pro. It was almost comical it was so big. ;-)
Maybe Apple's "really great" thing next year will be something like a stackable MacMini - You want 24 CPUs and RAID 15? Buy 6 of these boxes and stack them together with their Thunderbolt interfaces. You want portability? Take one with you. I suspect they're not that far ahead of the industry, though... With fast enough interfaces, and a sensible OS that can do distributed computing, it shouldn't be out of the question.
Oh, I wouldn't be surprised if they brought back the 17" in a Retina version - they're probably just not available yet. If someone really wants a 17", there are a bunch in the Refurbished part of the Apple store. The maximum resolution is 1900 x 1200.
FWIW. :-)
Cheers,
Scott.