I might have misunderstood what is happening, but looking at the block sizes it seems that most mining pools are sticking to the 250 kb soft cap, with BTC Guild being the notable exception. There are many blocks that are just under 250 kb, so I assume that pools are excluding certain fee-paying transactions to stay below the limit.
My question is, why are they doing so? Is the marginal cost of including those extra transactions indeed greater than the fee being paid? If not, what is their reasoning for acting in a non-profit maximizing manner?
The whole idea of Bitcoin is based on the assumption that participants behave rationally - i.e. profit maximizing. So what is going on here?