I always liked how Blizzard offered both PC and Mac versions of its games on the same CD / DVD. Now it appears that is what some digital distributors are doing. A friend of mine told me about Valve offering some of its games for the Mac on Steam like Half Life 2. I found this out when I installed Half Life 2 and registered it on Steam. I immediately had the ability to download the Mac version of the game as well
Just recently I noticed the same thing was happening on GamersGate. GamersGate had started offering Mac games, but now it appears that if you buy a game that is available for both PC and Mac you can download either version whenever you want. It is even retroactive because I bought a game for the Mac from GamersGate and now I can download the PC version as well.
I think this is a great trend for computer games in general and Mac gamers in particular. Keep supporting these sites and ask others (like Impulse) to support Mac gamers too!