Most European airlines seem to charge all their fees (including YQ) for an infant travelling on his own seat, but they do not charge those fees if you book an extra seat for an adult (e.g. obese passengers, cello players, etc). It seems that it would be advantageous for the adult to always book the infant as a lap infant, buy an extra seat for himself, and then place the infant car seat in that extra seat.

Am I missing anything obvious here?