Disregarding what is really a minimal expense, would the lack of an internal drive make you hesitate purchasing the retina display MBPs?
I had not used an optical drive in 5 years before I purchased this machine so it sure didn't stop me. And I'd been using a MacBook Air for about a year before I bought the Retina MacBook Pro they don't have optical drives either. And neither do most ultrabooks in the PC market.
There was one frustration, though: Microsoft does not offer a digital download version of Windows 8 system builder, only a DVD version. So I had to use my iMac to make a bootable USB drive from the Windows 8 DVD to install Windows on the retina. That is, instead of just making a USB drive from a downloaded ISO wasn't really any more trouble, but the point was I did have to use a DVD drive on another machine to get Windows on this thing.
And that was literally the only time I've used a DVD drive in about 5 years. I don't own any movies on DVD anymore either, just digital copies from iTunes, Amazon, etc.
It's only going to get more so that way, so I don't see why the lack of a DVD drive would stop anyone. And yeah, if for some reason you did want one, $80 is a pretty minimal additional expense if you're already spending $2500- $3000.