It was an issue of the things I wanted and what I didn't really care about.
If I went with a classic 15, I wanted the 1680x1050 hi-res screen. I also wanted to go with the 256GB SSD and 8GB memory upgrade, but would probably have done the swaps myself over buying it from Apple due to the price premiums on both.
With the retina 15, I could scale it to 1680x1050-esque (and, trying it out at the Apple Store, being non-native is not an issue). The base model had the 256GB SSD and came standard with 8GB memory. Also, built-in HDMI with audio out was a huge nice-to have opposed to using a dongle
With the classic, the optical drive on the classic was a non-issue. With the retina, I knew I'd have to get a TB-FW800 adapter since I'm very invested in external Firewire devices. For what I was looking for, the retina actually came out cheaper and had everything I wanted.
The difference was swapping one adapter for another, losing some weight, and getting a much nicer screen for slightly less money and a lot less hassle.
The only thing that made the decision one to think about are the first-generation jitters. But my 2006 MacBook Pro was also a first-generation model and ran like a champ until earlier this year, so that wasn't a huge dealbreaker for me either.