Donald Rumsfeld (remember him?) once said that there are:
… known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns — the ones we don’t know we don’t know.
It’s those unknown unknowns that tend to lead to the deepest trouble. For Palin’s critics, the significance of the year 1773 was just such an unknown unknown. The idea that Sarah Palin might be subtle enough to make a pun about “party” and “Tea Party” (not that it’s all that subtle, but they don’t even give her credit for that much wit), and that she also knows something about history that they don’t know, is simply incomprehensible to them. Therefore they fell into the trap.
Was it actually a deliberate lure? There’s been a bit of speculation in the blogosphere that Palin may have made the reference as bait, knowing that it would be irresistible to some. And maybe she did; after all, she’s a wily hunter.