Originally Posted by HTupolev

It would have been a perfectly reasonable road bike in its day. But, the bike as described in bicyclebluebook is in its original configuration, as a road bike with front and rear shifting; the craigslist posting you've linked is a single-speed conversion (possibly fixed-gear, but I'm not sure). If you're actually looking for a single-speed, and it fits you, and it's working fine, that's not an unreasonable deal.
(This is also the reason that the bike is only 20lbs.)

Even if you do want a single-speed or fixie, I'm nervous about the vertical dropouts. Most single-speed bikes without chain tensioners use horizontal dropouts for the rear wheel so that you can set chain tension easily with wheel position. When they have vertical dropouts, they need a mechanism such as an eccentric wheel hub that allows chain tension to be manipulated. Make sure that this bike has such a feature before you buy; otherwise, it's possible that it's only on craigslist because it's a failed conversion, in which case it would need significant extra work to get it running properly.