Even with a free carry-on, American Airlines bets travelers will still pay to avoid the cheap seats

Big U.S. airlines measure the success of their cheapest, most restrictive, fares by how many passengers pay up to avoid them. American Airlines next month is easing a key restriction of these so-called basic economy tickets — a ban on carry-on bags in the overhead bin — for travelers flying on its cheapest tickets domestically. But it's betting passengers will still pay for premium seats.