These dates have no real legal meaning, either. Only last year, 7th Circuit Judge Richard Posner reversed the conviction of a wily entrepreneur who'd relabeled 1.6 million bottles of Henri's salad dressing with a new "Best when purchased by" date. Posner decided that the prosecutor had unjustly condemned the dressing as rancid, rotten, and harmful, when in fact there was no evidence to suggest that the mature product posed a safety threat.
In the world of hunger relief work, however, food expiration dates give us quite a bit of pause, mostly because the food supply chain is so long and winding (not to mention unknown in some cases) by the time an item ends up in our hands. If you're curious, here's what the USDA has to say on the issue.