well, 50 percent out of one hundred would be average, so 0-49 % would be below average and 51-100% would be above average. So yeah, that makes sense. It's like saying 50% of the world's population is male. the other 50% has to be the opposite (female) or the fact that 50% is male would have be meaningless. There has to be a certain percentage of below average, and at average for above average to exist.