How long will unopened mayonnaise keep unrefrigerated?

According to "The Association for Dresses and Sauces," commercially available mayonnaise can be left out of the refrigerator for a long time and still be safe. Apparently, the eggs used in commercial mayo are pasteurized, killing bacteria like Salmonella. Also, they say, commercial mayo is sufficiently acidic to be unfavorable to bacteria that may be introduced after opening the jar. I always assumed that Salmonella was the prime problem, but if you think about it, mayo sits on store shelves unrefrigerated for a long time, and there's no reason Salmonella couldn't grow then. TADS also says the reason refrigeration is recommended by the mayo jar is to preserve fresh taste.