They get away with this because people just don't read. Strangely, that trick works even for a MAGAZINE....

I wonder how many people actually call/write/etc. to get their extra issue, and if the costs of paying the customer service reps to process the complaints is less than it would cost to just send everyone 12 issues. I'm guessing it's cheaper since most magazine prices don't even cover the cost of printing which is why they're full of so many ads.