I’m sure not everyone will appreciate this comic but it seemed appropriate considering the date.  Plus it sets up a plot point for later.

Alternatives to that punchline were:
Stan: Because Microsoft Camel Simulator 2001 hadn’t been released yet.

Stan: They tried stealing a blimp first but it kept bouncing off the buildings.

Stan: Because they wanted to get frequent flyer points.

There you go.

=Comic transcript============================
Deiter: Can you believe that it was seven years ago today that people used airplanes to attack a country on Earth?
Stan: You mean in the current timeline?

Deiter: Yeah, of course.  I guess I should say something when I’m talking about the past since we can technically be in any place at any time.
Stan: That was the best summer school class we ever took.
Deiter: But still…

Deiter: I wonder why they used airplanes anyway?
Stan: Because hijacking a bunch of camels from the zoo would have been a lot more difficult and way less effective.