I don't buy the bribe story. I've heard them make an announcement over the PA system during boarding that the "On board upgrade program was in effect." Then I saw one guy move up and sort the purchase out with a credit card.

I am also skeptical of the business seat-economy meal story as well. It's too complicated for one thing, plus if the upgrade price is over $1,000, they ought to darn well feed you the business meal. The true marginal cost is probably near zero, considering that the food has to be thrown out at the end of the flight.