If we had to put classical voice and pop voice in their extremes regarded differencies in vocal positions, I would say that it is in the way of treating the two positions in which we currently work (in pop for some dark and not high voices or when we want to give more structure to timbre even if losing some extension, we have just one position). In classical we use muscles of appoggio and sustain to obtain two vertical segments of those positions (the blending of registers) while in pop (and often jazz) we use the same muscles to give the illusion of two horizontal planes. Of course this is just the extreme pure, a number nearly infinite of ways of mixing of the two concepts is not only is possible but sign of a good technique and the choice of personal voice over a only academic one.