Mac AppStore should never happen. Stupid suggestion, if you ask me (I realise that nobody did).
1. Even if it starts off "in addition" to normal installations, it will move in the direction of being the exclusive source of Mac apps, which will lead to the absurd problems we've seen with iPhone rejections: who wants Apple playing gatekeeper? Not me, for sure.
2. Installing software on your Mac isn't difficult, it doesn't need to be made easy. An app directory might be useful, but PLEASE not in iTunes, it's already bloated enough as it is, perhaps on the Apple website (although there probably already is one?)
3. Why is Apple going to want to deal with all the hassle of dealing with developers, infrastructure, staffing etc?
4. People install apps on their Macs far less often than on their iPhones, and Mac apps are released less regularly, the experience doesn't need to be simplified to oblivion.
In this respect, I'd definitely be inclined to say "if it ain't broke, don't fix it". Until Apple comes out with a Tablet or something where finding installing apps is difficult/time consuming, then we might see the app store concept expanded.
I don't think it's a good move business-wise for Apple or for us as consumers.