Interesting, Maybe it has to do with the extra analyses that the brain performs on hearing. What I hear is not the raw vibration but a amonst other things a fourier transform of it. i hear a distinct pitch. The brain uses the harmonic overtones of sounds to group them together. When I feel vibrations with my finger I just feel slower or faster vibrations.

By the way, sometimes I hear a sound so low that I am confused whether I hear or feel it.