I think this has a lot to do with not having to sell anything to anyone. OSS projects are, in general, less concerned with converting users than commercial software -- you like our project join us and use it else 'meh'. While, it would be nice to have a shinny surface on oss projects, I think it is unnecessary.

As someone who recently (for work) switched from using Linux boxes to a MacBook Pro, I would generally take the less shiny functionality over the pretty pictures any day. (\cough\ keyboard shortcut to lock screen \cough\) :)