Because 95% of those people work with Linux, but not in it. OS X is BSD-based but close enough to make developing or supporting Linux machines simple. My entire infrastructure, thousands of servers, are all Linux, but most of the time I'm working on my Windows PC, and only occasionally do I break out my Macbook or Linux laptop. Love Linux, can't stand Apple, and I'm meh about MS except for gaming, but Linux as a desktop/workstation OS is still years behind OS X and Windows in ease of use. That said, I do not nor would I ever run either of those in any production capacity, just Linux.

Yes, assuming we're talking about DND, the player is asking if his total attack roll with modifiers is equal to or greater than the enemies armor class, which only the DM knows. If so, the attack hits. If not, it misses. An AC of 19 or more is pretty high for low level player characters.

This, but my pillow. Since I learned how amazing latex foam pillows are, I've had a hard time sleeping on regular pillows ever since.