Here's an MSNBC commentary about the decision. Apparently the public input was overwhelmingly opposed to allowing the cellphone calls.
The writer thinks the market could work in this situation by pressuring airlines to ban using the cellphones if the federal rules were someday lifted. I wish I could agree, but I don't. People often have to choose an airline (or have it chosen for them) because they live in a hub or need a particular schedule or for any number of reasons other than cellphone policies.
Without the government mandate there will also be pressure from workaholic higher-ups on the ground to stay in constant communication; if Larry Tate isn't on the plane then he could care less what the other passengers sitting around Darrin Stevens think when he calls Darrin. But he'll get upset if Darrin doesn't answer and Darrin doesn't want to lose his job. Spouses already feeling somewhat neglected might also take it as a slight if their calls keep rolling to voice mail.
Very important to have it government-mandated. Self-regulation won't work.