I think the 24 round magazine was developed when Glock ran its entry in the last U.S. Military handgun trials that Sig won with the 320.
You may be right about that. I've heard it's just a hair too long for the IPSC or USPSA rules, but I don't shoot those and can't confirm. If it's not for competition use though, there must be another reason besides it just being a nice size, and you've probably hit the nail on the head.
Regardless, they are a better alternative to mag extensions on 17 rd mags, and fit nicely in a pocket for walking around.
