Most celebrities fly neither private nor commercial, but rather sail forth on the power of their own beautiful, bouyant fabulousness.
As for what Alec Baldwin was doing playing Words With Friends on an American flight, here's what I can tell you:
It's more common than you might think. (The flying commercial part, not the Words With Friends part, though other celebrities have been kicked off of planes for refusing to turn off their phones, including Josh Duhamel.)
I spoke with Drei Donnelly, president of the Association of Celebrity Personal Assistants.
She says that who flies how depends on the success of the star.
In fact, Donnelly says, "lots of times, those flights are a part of their movie contracts."
Of course there are also stars who fly themselves around, such as John Travolta.
But sometimes, even for a big star, flying commercial just makes more sense.
"Some people don't like" flying private," Donnelly dishes. "My boss actually flies private domestically and commercially overseas."
Think of it this way, she tells me: "It's the difference between a renting a house and renting a room in a hotel. The commercial flight is full service, it's comfortable, you can walk around. "Sometimes you don't want to hassle with hiring your own crew; you just want to stay in a hotel."
As for exactly what happened, I have a good guess:
We know Baldwin was in Los Angeles to receive an award from People For the American Way. If the charity paid his way—and they tend to do that for celebrities traveling at their behest—they probably couldn't afford to accommodate Baldwin on a private jet!