Y'know for a issue that's 'not that big a deal', 31 replies in 7 hours is pretty impressive.
Two things (as someone that has seen many strange behaviors/ideas from working in corporate America and also with marketing reps):
1) You fail to take into account that the average gamer has no idea of the difference between a magazine or a clip. Or cares that there's a difference. Neither terms are used in great degree, even in movies where guns are prevalent. Most of the time, they simply say "I'm out!" when talking ammo. (If they are shooting 15 rounds without loading a revolver.)
2) Words cost money. Magazine is twice the length of clip. Might not seem like a lot, but when you're dealing with printed materials, every penny counts. And if you can shorten a book by 2-4 pages by misusing a term that everyone thinks is similar to the correct term, chances are you're going to go with the shorter term. And hope that the minority of your customers that would recognize the difference are forgiving enough to not make a big deal out of it.