Sure, but because the tech moves so fast, the components depreciate equally as fast, so it doesn't help much. You might get $50 for a card you spent $300 on originally after a couple of years.
And for some people, resale isn't something they think about when they buy a product.
People on other forums take raw performance very seriously. HardOCP, OCN, etc. they all have people on there that just want to get the highest possible benchmarks, so they get the latest and greatest to do so.
It might not make sense to you or me, but it makes sense to them.
Oh yeah, and about depreciation... I could have bought last year's model mountain bike for ~50% less than I paid for the model I just picked up. So the retail values do depreciate pretty considerably on those, too. I just had to get that shiny 2014 model. :)