Yeah i see your reasoning and i don't necessarily disagree with it. I think if Nvidia had made decent gains with similarly priced 7xx cards AMD's hand would have been forced. As it is they can bide their time and pick the moment they think is best for launch, which is clearly not right now. They also might be waiting for Nvidias full 7xx line up before releasing. This way they can alter things like clock speed to ensure they're faster.
I would have liked to see new cards, but to be honest ive just got a 7950 crossfire setup and seeing how this ploughs through titles at 1440p no new cards are needed, performance wise imo. So i can kind of see why they're thinking lets just wait a bit.
That said, i would like it if they came out with a brute of a card and took the single gpu performance crown back, but at the end of the day what does that matter. Price vs performance is AMD's trademark.