Our calculations on EM waves basically deal with harmonic waves and through such calculations and relations, we derive some relations and limitations for wave like phenomena. Of these relations are group and phase velocity of a wave. We impose some limitations on how great this velocity (e.g. for an EM wave) could be.
But how could (and why) we generalize such limitations ( like the one on the propagation speed of sinusoidal waves) to limitations for transmitting any kind of information?
Plus: What is the precise definition of "information" (which we always say it can not travel faster than C )??