You have to also take into account that in classic guitar it is not just the thumb on the middle of the neck that is correct but also that the thumb stays parallel to the middle finger, so that the tendons remain both relaxed and strong whilst the fingers move, allowing for maximum speed and stretch. This also necessitates the classical holding position (if you try it in the folk style position, your hand will hurt after a while).
That makes sense due to the big fretboard of the classical guitar where the style is such that you tend play fluently around chord positions. Classical guitarists don't bend, and their vibrato is in a nut to bridge direction.
That entirely reasonable logic doesn't make much sense with a skinny neck like an strat or an Ibanez (although the classical position works better on my baseball bat necked Tele) unless you are doing arpeggio shredding. If you are playing lead that is based on scales and bends (like most blues and rock guitar), the natural point of balance in skinny necked guitars is not with you thumb on the middle of the neck parallel to the middle finger, but at the side of the neck. So it is difficult to see how it is wrong, its just a different technique for a different style.
