That point can't be emphasized enough. The difference between gaming on a Mac and a PC and the difference between their target markets is incredibly important. Your average Slashdotter will buy a game, get a message about needing to update a driver (download a patch, tweak a setting, stock up on magic smoke at the nerd store, etc.) and not only look at it as an excuse to tinker under the hood for an hour, but actually enjoy themselves the entire time. The typical Mac owner not only doesn't enjoy tinkering under the hood, they aren't even aware that such a thing is possible or that there's even a hood. Never underestimate the number of people who want their software to plug & play as reliably as a USB device. Also, the people who are attracted to Macs because of their ease of use are also the ones who are least likely to spend hours and hours learning how to play a twitchy shooter and most likely to enjoy a game they can pick up in five minutes and play in short bursts rather than devoting an entire weekend to it.
A platform like Steam that integrates neatly into an OSX desktop and makes buying and playing games as easy as a mouse click or two might not sell a million copies of the Orange Box, but I can easily see sales from the Big Fish Games catalog going up a few hundred percent in no time. People who are willing to spend $3,000 on a Mac that's outperformed by a $1,000 PC are exactly the ones I'd be aiming my $10 game at.