Airline Fees: You Hate 'Em, Stocks Don't

In the past, because drinks were free, nearly every passenger had one. Now, carts no longer clog the aisles. Restroom lines have diminished. Less trash is left onboard. And it's no longer necessary to cater the aircraft every time it's on the ground.

Furthermore, "we've seen no market share impact," Kirby said. "We've looked at this closely."

AMR's(AMR Quote) American Airlines unit, which introduced the concept of a first-bag charge in May, has now been vindicated by widespread adoption of bag fees.

Three weeks later, UAL's United followed American, but the delay had allowed time for speculation that the charge might have to be rescinded if no one else implemented fees. "Four of our major competitors have now matched that fee, which I believe validates that decision," said AMR Treasurer Beverly Goulet.

Still, neither Southwest(LUV Quote) nor Delta(DAL Quote) has matched the move. Southwest, which carries the most passengers of any airline, touts its lack of fees in its advertising.

Delta, meanwhile, is poised to become the world's biggest carrier by revenue passenger miles pending approval of its planned merger with Northwest(NWA Quote). (A report Thursday said shareholders of Delta and Northwest are likely to vote in favor of the deal.)

"While we're always keeping an eye on what's happening in the market, Delta customers can still check a first bag for free," said Delta spokeswoman Betsy Talton.