I don't see all the fuss about it. He worked his balls off making it, so good luck to him.
I'm not really too impressed with valve cashing in on a 'fun' mod (given that the traditional mod stance was that if valve bought it, they'd sell it retail style but also leave it as free to the people who already own a copy of the game on which the mod is based), but I can't blame Garry for it; I'd do the same thing myself if I were in his position.
The only questionable aspect is the fact that Garry took donations and grants donators privileges.. and now all of that will probably be kicked away. This is a reason why I feel people should always think long and hard before giving anything in return for donations (as it puts a different complexion on things, it becomes more like 'buying' under a different name) or indeed taking donations at all. It creates conflicts of interest, expectations of support and it also means, as Garry said, petition online will probably explode as a result of this decision. Of course it's easy for me to say this (regarding donations) though because I'm not in Garry's position and, while I'm not even close to rich (monitor is giving out and I can't afford a new one) I do live fairly comfortably considering I'm a student with a tiny bank loan and no job.
Still though, say you have donated and now you feel you've been jipped, it's only $10.