I think this topic goes in ridiculous direction. My son stayed on my lap way after he had his own seat. You have a child-belt for turbulances (and statistics say lap-child is safer than kid in car anyway). Even the cots have seatbelts nowadays - some cots look like sleeper carseats.

Well, taxes for infants were close to zero, but post 9/11 and the oil-surcharges, I guess infants pay them. It's always better to pay the 10% fare directly with airline (symbolic compare to the "war tax" and "fuel surcharge"), since travel agents add their fee on top and then it looks like real money.