At the store that I went to for the 5S (Rockingham Park Mall in Salem, NH), only the first five folks in line got phones on launch day, unless they were on Sprint. Everyone that got in line fewer than 15 or so hours ahead of time didn't get a phone. I have no idea why that happened, but they literally came out when the stores opened, ushered in a the first five folks after asking them what phones they wanted, and told everyone else they could go home (while stating Sprint phones were still in stock). I got in line at 3am. And went home shortly after 8 with nothing...
So... that's why.
And that's the reason why I could never do the "line up outside an Apple store" thing. I can't imagine waiting in line for hours for a phone and when it's finally my turn, the store reps are like "sorry bro, you're SOL...all the phones are sold out. We got a few 5C's left tho...just let me clean the dust off of them" and also it's the fact that if you wait in line...you may get a phone, but it may not be the color and/or size that you want. And I don't want to just settle b/c that's all they had left, as opposed to getting the phone that I actually wanted.