It's 2014. Passwords need to be treated as a serious matter. Legacy system or not, there is no good reason to reduce keyspace. As others have mentioned, this is a sign that passwords are being made compatible with old phones without these letters available... and likely the passwords being reduced to numbers before storage. The prohibition of special characters also seems to corroborate this.

Furthermore, the poster below who showed screenshots of being emailed their password indicates JetBlue is storing passwords either in plain-text, or encrypting them (both just as bad), instead of properly cryptographically hashing before storage.

Honestly, if you add one extra digit/character to the password, that more than compensates for the loss of Q & Z. There are lots of circumstances where being able to work with legacy phone systems effortlessly would be most helpful. If you are taking passwords seriously, this might be the very last thing you worry about.

Or emailing them before they hash them.

I'm not sure about that. Sabre is an extremely (assumption) functional tool in an extremely niche market. That makes the barrier to enter it very high, and the barrier to rewrite equally so. Underneath the covers it could be a real piece hung together by duct tape and vacuum tubes, but why rewrite it if it's working and keeping planes in the air?

Because OMG HACKERS. Seriously, why do we have any security on anything?

It's nice to see these thoughts at the top of the thread. I get tired of hearing people in the security industry constantly smirking at "dump developers". They don't have a clue what it's like to develop real code with deadlines. They point fingers at others and call that an accomplishment.