JMich: There have been rumors about Aspyr coming to GOG, and I think they have quite a few of those games ported to Mac. Also, weren't most Macs back in the day PowerPC ones, thus their programs are incompatible with current versions?
snowkatt: yes but there are emulation layers
max os X 6.8 (snow leopard ) had roestta and emulation layer that allowed you to run ppc code on intel macs
i kinda doubt they were the only ones
there is also basilik II and sheepshaver
both are freeware but neither are easy to get up and running
And those two emulators require the original ROM files and all of their entangled legal issues :)
01kipper: It would be nice though if GOG would at least
tell us what is preventing the games' release on Mac (may be different for different games):
1) GOG is working on it
2) Not possible for legal reasons
3) Not possible for technical reasons
2 and 3 are usually the most common culprits as to why particular games or versions of games are not here.