I would guess that the machinist may not feel it's a superior condition to leave them 020 in the hole(aside from maybe the reason stated) but that it isn't going to make enough of a difference to cut it. Besides, like Blue said, if compression's good at 020 then why cut it and then have to make it up somewhere else like dished Pistons or thicker head gaskets. Don't over think it. It does matter how much, exactly, you're talking about too. My latest block was just squared and I was lucky to keep all the Pistons just barely below deck. In fact one of them ended up a couple of thou above. So be sure what the measurements are before you make any decisions.