Don't you find it dissapointing that every single Linux distribution maintains it's own package repositories whether it be portage, rpm or dpkg based?
Not really, to each their own. Some distros prefer to have the absolute cutting edge packages in their repos, other prefer to use time tested packages. There are also differing ideas on how software should be packaged or what compile options should be used.
Have you ever wondered why most distros repackage the binary ati/nvidia drivers instead of using the installers ati/nvidia provide?
Because the nVidia installer is an absolute pain to use? telinit 3, run installer, can't find a precompiled kernel module, needs to compile one, go edit your xorg.conf, hope it all works... The Ubuntu way just works.
Third biggest problem with Linux: Ten million different distros are all maintaining packages for the same software. In the wonderful world of windows any idiot can build an MSI package and it'll generally just work on a wide variety of windows installations
(barring any other technical reasons that are specific to the app itself) without any modification.
The biggest issue I have is architecture issue, especially when running 64-bit distros. It's sometimes hard to find precompilled 64-bit binaries, but Windows seems to be having the same issues in a number of cases. Other than that, the package issue isn't a
huge concern. Debian-based distros can either use the native dpkgs or handle RPMs with alien, but I've only needed to actually install an RPM on Ubuntu once because I can generally find a suitable dpkg.