You're not seeing the forest for the trees here...
You are 100% right...nobody forces them to buy a ticket on their airline, but things like charging them for a farking beverage reverberate in people's minds when it comes time to do so again in the future.
Those people will take their money elsewhere if there are other options, lowering your company's revenue and endangering that job you have and that money you earn. What is the potential cost of the potential upside?
Americans hate feeling nickel-and-dimed. Quietly raise ticket prices across the board $2 and VIOLA no problem whatsoever...but put out a press release saying beverages are no longer complimentary and that a $0.25 can of soda now costs $2 and you get mocked on live national TV.
The only possible upside I can possibly see to this is maybe, just maybe, US Airways will get rid of that gawdawful coffee they offer and brew a real brand like Dunkin, Starbucks, or even Folgers...