Price fixing is highly illegal, they would be fools to go down that particular road. Intel especially, with all the fines they've been hit with in the last 20+ years!
Price fixing is very hard to prove. There might be no written agreedments between the companies but they copy paste their competitors' prices, so you get the same end result.
What's worse, is that intel might try their dirty tricks, so everyone starts to buy only their cards, while AMD would be denied from selling their Radeons. The same what intel did in the Athlon 64 days.