I don't know if firmware can fix gamma. I also don't know what Panasonic's history is for fixing things like this with firmware either.
However, this problem seems to be limited to THX. Being the owner of a G25, which I adore, until someone tells me, or I see, that theres a significant difference in shadow detail/contrast, no flashing blacks and no flashing luminance I won't believe that GT30 is worth the extra $$ when considering the ST30.
Also, I'm not convinced that there's not a set out there as good or better in the same price range when all things are considered including user tools.