Because the bad news is priced in... and wasn't as bad as some people expected.
The world's chips are sold between Intel and AMD... Intel's numbers are a predictor's of AMD's also. What one missed, the other got. Plus AMD owns ATi, which they're still digesting.
If Barcelona is any good, Intel may have a problem, especially with AMD's new ability to incorporate cost savings and tandem development of CPU and graphics now ... something a lot of people count on. It was always a given that AMD would recover, then exceed.
You are no longer talking about just AMD, as it was just a year ago. You are talking about 25% of the world's chip market, and 60% of the world's graphics market now in 1, hopefully not bloated, company. It was only a matter of when and by how much it would recover.
I didn't think it was possible it would go below $10, and it never even went below $12. But with a shortage of good news for the sector, I don't think it's going to quadruple just yet. But it will.