Small studio needs funding so they announce it early.
Big studio/pub has it's own money and can wait to announce it at E3.
I can see why they should have waited, but game cycles take 2-3 years these days, so if they want to get PC2 out they have to start on it now.
But people put their feelings into things and the reactions follow.
AMD users have a good reason not to buy. I have a GTX 980 and it has ran smooth since I bought it three weeks ago.