Parroting what he read from some other posts.....
Linux derives from Unix, which has robust multi-user capabilities as a core strength.
Some directories were intended for "system" files--others for things of more interest to users.
You can find */bin and */sbin directories all over the place--it is simply where the binaries are kept to avoid having them clutter up other directories.
I think on TLDP (The Linux Documentation Project) there is a writeup on what goes where in a "typical" Linux directory setup.