IPhone's don't have as much GB as they say?

Two years ago I got an iPhone 4 that was supposed to be 8GB, but when I got home and hooked it up to iTunes it said the capacity was only about 6GB. I figured it was a fluke and didn't care that much.

Today I just upgraded to the 5c which was supposed to be 16GB, but the capacity is only 13.25GB… Why does this happen?

Yes, the Operating System (IOS) takes up space, so 16gb - IOS = 13 gb's.

Because some of the memory is already used up on default apps like the iTunes app, and the music player app.

So you think iOS just runs in the thin air around it?

Yeah its annoying. They should make the size 16gb, 32gb, etc. After iOS. It's really not that much of a diff at 32gb but it is at 16.

It comes with 16 GB of memory, not 16 GB of *available* memory.