Did not want to sound like a jerk. I actually think that your point is interesting, but one can go much further than an AFL curse. For example, note that 8 teams (Steelers, Cowboys, Niners, P•ts, Raiders, Packers, Redskins, Giants) have won 3 or more Super Bowls, for a total of 30 titles. That is more than 2/3 of the total championships in the hands of 1/4 of the current franchises. If you add in the franchises who have won twice (Dolphins, Colts) you are talking about ten teams (less than 1/3 of the present franchises) holding about 80% of the titles. For all the talk of parity in the NFL during the regular season, championships are rather thinly spread around.
What does it all mean? That it is hard to win in the NFL, I guess.
Edit: I forgot to include the Broncos, who also have won twice...
Also consider this: outside of the Niners and Jets, every team that has won a Super Bowl has also gone at least once and lost, and the Jets have only been once anyway, thus further demonstrating how a relatively few teams have been to most of the SBs.