In Australia, print classifieds are still big business - bigger than online ones. How is that the case when, for instance, Craigslist in the USA has all but killed that sector of the newspaper game? According to my highly-scientific workplace poll (three guys and me) it's about price and visibility. If you want to sell a second-hand couch, you have a couple of options for putting it online, which already means you don't know where people will be looking, and when you get it there, everyone is after such hardline bargains that it looks like every seller is dreamin'.
If your price is more than $50 for anything in your house, you probably won't sell it. If it's smaller than a kitchen appliance, it had better be $10 or less. So why would you bother? The time and effort to sell something that way online is worth far less than the decluttering satisfaction you gain by just chucking it in the bin. Selling in print just doesn't have that same instant-gratification, search-and-die feel of online selling, so you're more likely to get a sale to someone who isn't a rabid uber-bargain-hunter.
Mokalus of Borg
PS - We may be wrong.
PPS - Especially since we did no research at all.