EXACTLY! Thank you so much for clarifying the
very question I have tried to get answered.
It *seems* the GM can be upgraded to the full
production release via software updates based upon
past GM releases (Snow Leopard) -- but nobody is
positively sure and nobody is quoting the exact
release notes that accompany this GM release.
I'm not sure why this issue has become so confused. Basically, the GM is released by Apple with the hope that it can be the final retail release. A brief period of testing follows it, and unless any glaring bugs are found, it becomes the version sold publicly. Naturally, if that happens, you'll be able to update to 10.7.1 and beyond with no problem whatsoever.
The only question mark, then, is whether or not this is the only GM release. If you assume it is, and that's a reasonable assumption, then you won't have a problem. Of course, no-one knows for sure at this point, so it's a gamble, albeit a minor one. Worst case scenario is you have to reinstall over the top of the previous GM, but after four developer previews you should be used to that by now, ha.