Hmmm...sorta yes, sorta no
If it's a bike with a good following, used ones will sell uber-fast. I was trying to help a buddy of mine find a used KLR-650 in the 2002-2003 green color. Every one we found for a month got snapped up within a day or two of them being advertised. Not even widespread advertising, either! Just a post on the for sale page of a KLR650 forum and whammo, it's sold. My buddy ended up buying a new 2004 KLR650.
Sport-tour riders seem to hang onto their bikes longer so the used market is probably small, but when someone does sell one, I'm guessing they'd sell pretty well as long as the right people looked where the ad was.
Oh yeah gotta love the internet. Both my bikes I found on the 'net. If it wasn't for this surfing stuff I'd never have gotten into motorcycling at all.