Some package management (apt) would be better if it would be easier for 3rd party vendors to get into the sources.list. For now you either have to get users to edit that file by hand (for which they might not even have the rights) or you have to use another installation mechanism which avoids the package management to which they are used and lose the advantages of stuff like upgrade. Maybe there should be a sources.list per user which allows normal users also to install software and distros could be set-up to work with a certain file-type in a way that if you click it on the web, then a default installer goes up which guides you all the way through the installation.

Right now the situation is that if you want anything that's not in the "official" package repositories (probably the majority of software ...) you are getting into a world where installation is harder than in any other OS. And that is true as well for open-source applications (you want newest blender or one that is months behind?) as closed-source applications (which simply don't get into official repositories anyway).

I also tried using one of the binary installers for a while, but when it stopped working with newer distros (my application still worked) I guessed that tar.gz and zip are for the moment simply the best I can really offer and that's still what I'm using for now.

That is pretty much the problem. The only software that installs easy (in most cases) is the "distribution supported software" (in the version(s) currently used by the distribution that is).

I guess one of the questions to answer about ease of installation is what makes Linux software different from the majority of OS X software.

[note] OS X does have a package format for more complicated stuff