Let's travel back to
1962, where we discover what may be the very
first attempt of a reader to catch a
Marvel comic making an error, in
Fantastic Four #4:

Wait a minute!?!?
5 bucks?!? That's much better than a
No-Prize!! (Not to mention roughly
$35 in 2010 dollars!) You could buy
41 12¢ comic books with 5 bucks, and have change left over!! (Sad fact--$35 bucks would only get you
11 2011 comics, and that's if they were all $2.99...)
Well,
Stan came through, and kept the promise (at least to one reader), as we see in the letter column of
Fantastic Four #6:



For the record, the
Michael Snell listed first there is no relation to me (although that is my father's name...). Still, I embrace the coincidence as a meaningful portent of my love for the
FF...
With that kind of response, no
wonder they switched from cash to No-Prizes.
(And no, before you ask, at that early point
Sue had
not yet manifested the power to make objects and other persons invisible. So no, that wasn't the "
correct" answer, and no, you
ain't getting 5 bucks...)
Of course, these days Marvel--and even
Disney--would be bankrupt if they had to shell out $5 every time Marvel made an error...