A better approach is having good defaults, and letting the user add associations as he needs. That way the control is returned to the user, and he will feel confident updating the list of associations. Bonus points for multicast and not being restricted to one string format.
I would love to be able to eschew the web tech altogether, since we can all agree that HTML/CSS/JS is a terrible solution for building rich applications. But how else do I deliver my software without making users jump through download + install + update hoops?
But yes, I agree. Many people use windows, and the download-install-update circus seems to be driving people to develop web applications.
Also, the reason package managers suck is because.. entropy. See Joe Armstrong, The Mess We're In http://www.youtube.com/watch?v=lKXe3HUG2l4