Tubes can only make a difference to the sound when they're used on the output stage, i.e if they are right before the signal hits the speakers. When its part of a system like that, its just a gimmick, they run the tube on the input signal (which does nothing except add distortion) and then feed it into a solid state amp.
BTW, just to clear up any confusion, DONT compare a tube guitar amp to a normal tube amp, they are COMPLETELY different things. The Guitar amp is designed to add even order (warm) harmonic distortion to the guitar signal. You dont want that in an amp thats REPRODUCING music and not CREATING it, because its adding something to the signal that isnt there in the first place