Dont forget add unix flavour here...

There are more than our fair share of unix.
Adobe (offical)+ debian = oh?? broken ... this is because Adobe hasnt
got a clue about Intellinux.

To many manufactorers are producing slightly different versions this is
why the programmers of things like flash should make their installers
customizable so that operating system makers can provide customized
versions.

Windows reg makes it easy for programmers to find where reqired
applications are placed.