Don't worry! I'm sure Sega's working on a Digital TV tuner for us right now! I've never heard of anyone I know actually using or even owning the GG TV Tuner. I think in Japan PSP or Nintendo DS has a DTV tuner.
The Game Gear tuner has a composite A/V input, doesn't it? You can hook up one of those coupon-exchanged DTV convertors. Maybe they'll make one that runs on batteries too.