Stupid question: Why are miners including 0-fee transactions in blocks at all? AFAIK, they can refuse to do so regardless of max blocksize.
Absolutely correct. Though the default client allows for some zero fee transactions and miners may choose to keep doing so because they feel it's good for Bitcoin at this stage.
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Including in Blocks
This section describes how the reference implementation selects which transactions to put into new blocks, with default settings. All of the settings may be changed if a miner wants to create larger or smaller blocks containing more or fewer free transactions.
50,000 bytes in the block are set aside for the highest-priority transactions, regardless of transaction fee. Transactions are added highest-priority-first to this section of the block.
Then transactions that pay a fee of at least 0.00001 BTC/kb are added to the block, highest-fee-per-kilobyte transactions first, until the block is not more than 750,000 bytes big.
The remaining transactions remain in the miner's "memory pool", and may be included in later blocks if their priority or fee is large enough.
This section describes how the reference implementation selects which transactions to put into new blocks, with default settings. All of the settings may be changed if a miner wants to create larger or smaller blocks containing more or fewer free transactions.
50,000 bytes in the block are set aside for the highest-priority transactions, regardless of transaction fee. Transactions are added highest-priority-first to this section of the block.
Then transactions that pay a fee of at least 0.00001 BTC/kb are added to the block, highest-fee-per-kilobyte transactions first, until the block is not more than 750,000 bytes big.
The remaining transactions remain in the miner's "memory pool", and may be included in later blocks if their priority or fee is large enough.
