Absurdly priced menu items are more than a publicity gimmick. They're an application of “anchoring,” a cognitive phenomenon discovered by psychologists Amos Tversky and Daniel Kahneman in the 1970s. Whenever we try to estimate a numerical value, we are unconsciously influenced by related numbers just considered. In this case, the diner in a touristy Manhattan restaurant is trying to decide how much he or she can afford to spend. The familiar prices back home don't apply.
That diner isn't going to order a $69 hot dog, but might happily opt for an $17.95 cheeseburger. The hot dog makes the cheeseburger appear reasonable in comparison (even though $17.95 would be a ridiculous price for a cheeseburger almost anywhere else). In scores of careful laboratory studies, price contrasts like that affect decisions. Restaurateurs and consultants believe it works on menus, too.
Anyone interested in the psychological tricks companies employ, should read Poundstone's book Priceless: The Myth of Fair Value (and How to Take Advantage of It)