GNOME and most other projects are no different - they just happen to have one or more companies who do the polish users need/want (eg Red Hat and to a lesser extend SUSE for GNOME, the last few years). KDE once had that (SUSE before it was acquired by Novell) and it was far better in terms of user experience.
Volunteers don't do that, period. Not KDE specific at all. KDE IS a project with amazing technology, which is years ahead of any other Desktop thing (be it Windows, Mac or anything Free). It just has nobody doing the polish. Maybe Spark can make a difference there, or somebody else can find a business model - eg 'Balsam Linux', an openSUSE derivative, has afaik such ambitions. I hope they or someone else succeeds at this... Too bad it didn't work out for Kubuntu/canonical (although I personally doubt they ever really tried).