One thing that's always been really annoying about Mac apps has been the lack of an update system. Most Mac apps check for updates on launch, which is spectacularly annoying, since you're being prompted on the update right when you're most wanting to use the app, and it makes it really hard to make sure you're up to date (since you'd have to manually cycle through your Applications folder).

Compare this to Linux package managers, where a simple "sudo apt-get yada yada" line or two updates everything on your system, whether first party or third party.

Insofar as a Mac App Store solves that problem, great.