You're lucky you're getting out when you are -- like another guy said, "it's a matter of timing."
In other words, some miners are cashing out the value of their systems BEFORE the flood of cards hits the market, which will happen very soon.
They want to sell their 5870's and 5830's while they can get top dollar for them -- while there are still some "slow" people who think we're still in a Bitcoin Mania bubble.
As I've said several times -- in any bubble, you have people who are quick, average, and slow to figure it out. I'm quick. Some average people will soon catch on. Last of all, the idiots will catch on -- after it's too late. They'll be caught holding the bag (having just bought a $160 card that's worth maybe $90 for mining purposes).
The days of getting $140 for a 5830 are numbered. The number of dumb 17 year olds begging mom for a good mining card is limited. Those kids are never going to make $150 or $160 from a 5830 -- ever. It's too late in the game for that. Maybe a few weeks ago -- but not today.