Ok, I'm not even gonna say anything negative or otherwise about GameSpy since it's that obvious anyway. Suffice to say I still remember the bad ol' days of going through their "company" to get anything UT related, which is why I thank the Lord for BU.
I do know there's plenty of alternative game browsers like ASE and Qtracker so PC gamers at least aren't stuck with GS or the GS-lite in-game browsers, so there would have to be something like that for Macs as well. The problem here is that the game developers are getting screwed. If I were a developer I would seriously look into alternatives like an open sourced program such as QStat. All else that's needed is a master server or better yet have a small app where people can have their own master servers.
And as for Mac gaming in general, well don't dismiss the 10% niche market because that's 10% more than usual demographic market. And yes, stuff like Mahjong are still games even though you don't gib people to bloody pieces...