There is a significant difference between a TV signal and FM signal. Because the FM signal occupies a far narrower range of frequencies than the TV signal, the FM signal is affected by noise less. This translates into the FM receiver being able to be sensitive to lower signal levels than a TV tuner. This is fundamentally true regardless of whether the TV signal is analog or digital.
If you're interested,
http://en.wikipedia.org/wiki/Nyquist...mpling_theorem &
http://en.wikipedia.org/wiki/Johnson...3Nyquist_noise are jumping off points to do some research on the relationship of noise and band-width's effect on the information capacity of a theoretical 'information channel'.