I'm said this before but I'll say it again.
The iPhone 5c isn't intended for users of this forum. Yes, there are those of us here that bought one (me included), but in reality the iPhone 5c is for the "average" iPhone user. The soccer mom or teenager or average person buying a cell phone. The kind of person that doesn't know what "64-bit" means. The kind of person that doesn't watch Apple's Keynotes and likely doesn't even know that Apple makes products outside of the iPhone and iPad.
The iPhone 5c is for them. These are the folks that buy a new phone whenever they need one: Whenever their previous phone breaks, is stolen, or they just decide to get a new one.
The iPhone 5s, meanwhile, is for the Apple fans and tech geeks. The kinds of guys and gals what will sacrifice an entire workday to wait in line to get a new phone. The kind that drools over spec sheets and drop tests and every bar graph and pie chart that they can get their hands on.
These are the folks that buy their phones on the first day. Some will buy a new phone every cycle, some will buy a new phone every two years. But these are the customers that pay attention to tech news and plan their purchases accordingly.
And this is why the 5s is currently sold out but the 5c is still in stock. It's because the folks that want the 5s want it NOW, while the customers that will end up purchasing the 5c likely don't even know it's available yet. They'll buy them as they need them, not just because they want them.