Likewise, miners have all kinds of perverse incentives in theory that don't seem to happen in practice. Like, why do miners include any transactions at all? They can minimize their costs by not doing so. Yet, transactions confirm. You really can't prove anything about miners behaviour, just guess at what some of them might do.
The fact that miners include transactions at all is a great example of how small the block limit is. Right now the risk of orphans due to slow propagation is low enough that the difference between a 1KiB block and a 250KiB block is so inconsequential that pools just run the reference client code and don't bother tweaking it.
I don't think that was the point Mike was making. Rather, the cost of computing the hash of a block is directly proportional to the size of the block, so doubling the blocksize is like halving the hashrate for a miner. Thus, while rewards for finding blocks are large compared to fees, it is more profitable for a miner to mine a block as small as possible because his effective hashrate increases and he is more likely to find blocks.
What this says about miners (or really, pool operators) is that either:
- they're too lazy to change the code
- they're not arseholes / aren't purely motivated by short term profit
- they realise that by mining empty blocks, the usability of bitcoin will reduce, hence the market price, hence their profits