Why is my iPhone 4s capacity less than what it is claimed on the box?

I'd just gotten into the iPhone trend two weeks ago, so I'm still learning. I was just loading a video into my computer and I realized that the capacity shown on iTune doesn't add up to the amount of capacity that the box has claimed. In iTune the capacity shows to be 13.6GB, yet the bar located at the bottom (the one that shows how much memory the apps or photos are taking up), the capacity totals to 13.71GB. However, in the box, it claims that the phone has 16GB. Can someone please explain it to me.

Software updates bud.

Because the software takes up 3GB.

Your phone IS 16gb, however donor forget that there are already per loaded apps, such as the settings and all the menus and sub menus. Plus there are things on the phone you can't see that makes it run such as the OS. This does take up that -3gb of space that you're concerned about.

Ok, for starters it's called iTunes, not iTune. Your phone has software and other stuff that came on the phone when you first got it.

Because its apple and they always try their best to screw you over.

Formatted space is always less than actual space
iOS takes up a lot of space as well

A 16GB iPhone really only offers the user around 14GB of storage space; the other two gigabytes go towards the operating system and stock apps.

So now your 16GB iPhone offers you fewer than 12GB of storage space.

That's how they all are. 16GB is the limit but you only get 13.71GB or so due to iOS itself & other files taking up some of that space.
Not just iPhones or Apple products btw. Any hard drive based device does that. Your computer being one of these.