Why don't I have any storage?

So I got an iPhone 4S on Halloween 2012 and it's now February and I have "0 bytes available" it's 16g and I only have 11 apps, music taking up 1.0GB, pictures taking up 806MB, video star(an app I have) taking up 230MB, videos taking up 164MB, mine craft (an app I have) taking up 151MB, subway surfers(an app I have) taking up 73.3MB, Instagram taking up 51.4MB, then other apps 36.5MB, 29.1MB, 21.8 and 2.8, also it says "0 bytes left, 13.5GB used" I thought my phone was 16gb!

It's like that with all apple things. I have an iPhone 4S 16gb and I only have like 13 gb of stuff but its actually full. So 16 basically means 13 and 8 means 6. Stupid right? I guess it's all the information in it before you put anything on it like everything that makes it work. I don't get it either. It's confusing. Sorry