If you packaging partisans manage to convince developers of the merits of your position, the individual packaging method won't be easily available: it'll be "wait for the OS maintainers to decide to include the newer version" or "make; make test; make install" (i.e., be your own packager).
The developers are still free to package it themselves and distribute installers as .deb, .rpm ETC. If they have a dependency not available in your package manager (or to old a version), they can either also send you that, or have you add their PPA. The only significant problem I see is that their is a fragmented market of packaging systems, which makes it difficult for individual developers to target everyone. Of course *.tar.gz is a good universal installer for when someone doesn't use a major package manager.
We "packaging partisans" are just saying we find classical packaging superior to the every-piece-of-software-on-its-own model, not that the latter isn't an OK fallback if there is no package.
