I think I'd rather have the "walled garden" where developers have to pay a nominal fee to get in for the store built into the OS.
I haven't really used the App Store on OS X much at all, but I think it's a good thing to have some place "safe" that family members can buy from without me worrying about them infecting the system with malware etc.
Where a "walled garden" becomes a problem is when that's the only option for installing apps, like it is on iOS.