It's because the dumbfuck, luddite administrators receiving the applications only know how to print them out and deal with a hard copy. So the programmers have to accommodate their masters' stupidity.
New rule: "If your butt doesn't fit in this box, you will have to go first class or buy two tickets."
That's _already_ the rule. The issue here is that he normally buys two seats (for his own convenience, not because he can't fit into a single seat), but he ended up getting on an earlier flight (on standby) that was full and didn't have an extra seat available. The pilot assumed that Smith would be an inconvenience for other (adjacent) passengers just because he had initially purchased two tickets -- despite the fact the he was able to fit within the confines of the seat and lower the armrest.
RTFA; it's not that fucking hard, people:
Life would be so much easier if we could just look at the source code. -- Dave Olson