It doesn't seem to be so bad right now, but part of this may be due to my insistence on getting at least 4GB of RAM for a MacBook Air, which was hard to find on the used market.
[1]Random idea for a website/service: Computer reliability statistics by model/year. Could be really useful for people in the market for used machines. Not sure how/where you would get the data though. Seems like forums are overrun with anecdotes, but actual data is few and far between.
Macs are quite variable in terms of good models and bad models. This seems to apply to both laptops and desktops. Unfortunately. I also haven't heard of a website or service that has the reliability statistics you want.
You didn't mention Applecare. It is transferable and is for 3 years. So if you buy a 1 y/o machine from a hipster who wants to upgrade, you would be covered for the remaining time.
Perhaps the used prices are propped up by a high number of units dying.