It doesn't work as well for proprietary software, but it's still feasible. Adobe doesn't develop the Ubuntu flash package, it's Ubuntu's job.
While it's always nice to find a package for your distribution on upstream site, demanding (not just suggesting or wishing) that developers package their own software for your distribution is wrong and goes against that agreement.
Not only that, but most of the games in the Humble Indie Bundle have open sourced their code, so nothing prevents a distribution to package at least the program, and offer to prepair the whole package (program + proprietary data) so upstream can offer it on their site. The games in the HIB are doing far better than a proprietary game offering binary Ubuntu packages, since the latter don't let you fix security issues, and only offer you the appearance of good service.