So the package repositories are nothing but convenience for the end-user.
Isn't conveniencing the end user kind of the goal of all software? Surely there is value in tracking dependencies and conflicts (and in avoiding problems that can arise without these things) that should not reasonably be dismissed as "nothing but convenience". Perhaps I could say the same of every useful thing you've worked on.
I'm not debating that nor am I dismissing that package repositories provide tremendous value to the user. However, the parent asserts that package repositories act as a gatekeeper, thus making it harder for users to install software that is not in the package repositories. That's not true, since linux/BSD/MacOS package repositories just enhance an open system. In that context, they're mere convenience, not a requirement.
External dependency hell. Not in the repository, not invited.
Honestly, I haven't used windows(other than in VMs that is) since windows XP. When vista came out, I went "fuck that shit" and switched to ubuntu(then gentoo and eventually settled on Arch). Now my personal laptop is still running Arch and for work I use a macbook and an iMac(Hate the fact that you can't develop for iOS without OSX but meh, gotta be pragmatic).
TL;DR; I'm no expert but I guess they're trying to remedy that with the store thingy in Win8.