I was a painting major in undergrad, finished in '97. Didn't take any computer classes, but I did take one typography class - by the time I got my first job with a computer a few years later I didn't even remember how to turn it on. I fell into retouching through a friend of a friend who owns Q Studios here in NYC, and Joe (owner) trained me like an apprentice - first drum scan, then dust n bubbles, then small cloning, etc. Color was the last frontier, and still is, after 9 1/2 years. Always more to explore and learn with color, where compositing, silo'ing, etc is what it is.
I took two years out and got an MFA in studio art from '02-'04, then hopped back into the commercial world after designing exhibitions at the Museum of Natural History for a year.
I don't know about you photographers-turned-retouchers out there (except Richy) but I know that painting, life drawing etc. factors daily into my retouching - light, color, anatomy are the basics, and if you don't understand these then you will always be limited as a retoucher, I would think. Numbers can only take you so far.