Hi Graham,
it should be there as an update … and yes, it works fine on 10.6.8 (at least on my 2 Macs). Maybe you need to reset the AppStore app (delete the prefs, clean out user caches etc.) and try again. The apps you bought will not be lost by doing that. I think there's info on the web on how to fix this issue of missing updates in the AppStore.
Most of the acute Facetime troubles come from the ongoing lawsuit with the patent-trolls of VirnetX. So, I'm afraid there will be more bumps ahead due to Apple's remodelling of the whole Facetime infrastructure while running it.
Regarding the other problems, you're unfortunately right! I'm also one of the "little people" who uses his Macs to earn a living. A former research-fellow, I now work in scientific publishing and do everything from scientific papers, posters, videos, slideshows, up to doctoral theses, text books and habilitations. With the advent of the iPhone the professional Apple products started to become less and less useful for me. The Mac hardware also started to deteriorate due to bad design decisions, e.g. using "bathroom-mirrors" as displays, built-in obsolescense ("keyboard defect? throw the MacBook away"). But worst of all, the MacOS started to become a dumbed-down mess, topped up with lots of useless eye-candy.
E.g., with MacOS X 10.6.8 + some plugins I can view, edit, and convert lots of different video and audio formats (even FLAC and other high quality stuff) via Quicktime. On a brand-spanking new Retina MacBookPro I get video output options: iPhone, iPad, Internet … completely useless! And of course, all the old plugins and tools to work with the good codecs don't work anymore on Mavericks. Macs are on their way to become high-priced, but utterly useless TOYS … and they're almost there!