Originally Posted by scalesusa
I've wondered about this. I'm pretty sure the root cause is Canon raising the MSRP on their lenses over time, driving up street pricing for new lenses, and enabling owners to sell their used copies for much less of a loss than depreciation would otherwise mean. The other factor is that while many buyers care about the date code, many don't, and as such, an 'old' used lens (e.g. UT) is not substantially cheaper than a relatively 'new' used lens (e.g. UW).
Of course, it's all relative, but as Denise found out pretty recently, if you buy a new L lens and try to sell it relatively soon after purchase, you'll take a significant hit. If you wait a few years, the then-current used prices may well end up at around the prior new price, and you've gotten a few years' use from a lens for effectively no cost.
But then, I'm a pack-rat - the only lenses that I've sold were lenses I bought used, at such a good price that I took no loss on the sales (the opposite, in fact, which eased the 'pain' of selling them). I'll have a 'real' decision to make if I get the 85mm f/1.2L II - keep the 85mm f/1.8, or sell it...