What?? It's cat and mouse, has been for decades, still will be for long. I've yet to run a game and say "Well, this graphics hasn't improved for a few years now." If anything, I'm thinking about the newest AMD and Nvidia offerings and how I can get my hands on them. If hardware has reached a point of being able to sustain what the programmers dream off, then why continue releasing high-end premium gaming new cards that ARE being bought?
Sorry, but that stopped being a reality after the Quake engine. What's happening now is the same thing that happens in any business: trickle down to keep business alive.
That's why you keep buying high end GPUs to catch up with what's already outdated for developers.
Edit here: just research how long the Quake II engine's been used since its arrival, and how many companies licensed and or based their engines off of it. It's old hat. And ID's next engine is a good two years outdated as well, but when it's implemented in games it'll be "fresh".