[zorr]

For base packages like desktop environments, tools, libraries, popular applications, etc, yes. But I don't think they should be responsible for every end-user third party application. It's a massive waste of time for everyone involved.

[JohnFen]

I think they should be responsible for the packages in their package manager. That's the main thing that distros do.

For software that they can't do this with, or that isn't worth their time, they just omit it from the package manager.