I live in Chicago, and while I'm also not happy I can't get standard capacity mags from him, I reserve my ire for the people who truly deserve it: my corrupt city government. I can't blame a small businessman for not wanting to risk his livelihood on an uncertain market, especially given my city's reputation. FUD works for a reason.
For those who don't know: all handgun regulations are now the sole domain of the Illinois state government, which has lifted all magazine capacity limits as part of the same act which legalized concealed carry three years ago. However, that has not stopped numerous localities (like Chicago) from passing its own laws limiting capacity, even though they are explicitly forbidden to do so.
So we have unenforceable laws on the books which directly contradict the state laws which explicitly preempt it. Even though standard cap mags are absolutely legal in Cook County, but I can't expect a retailer to wade through the morass of FUD to figure that out. We have the same issue with numerous online ammo retailers.