Will mining centralize around one single miner? No one knows. This is why Bitcoin is still a risk.
But if this doesn't happen--if there remains more than a single miner--then the fee market does exist.
I think the point of contention is really about this conclusion.
My understanding is that it may also happen with several miners if they have an incentive to synchronize their mempools (with a mechanism like IBLT).
See this post written by Gavin (chapter "Will this skew incentives ?" of
https://gist.github.com/gavinandresen/e20c3b5a1d4b97f79ac2)