Yep, good point. I think it's a consumer expectation problem. We are used to installing desktop software by first downloading a package from the author's website. Linux distros break this expectation.

In mobile we have the opposite expectation. We expect to go to the platform's store and get the application.

Perhaps the introduction of the Mac App Store, Chrome Web Store, and (soon) Windows store will change the expectation a bit, and the Ubuntu way (which has existed as long as it has) won't seem foreign to people.