Why do some areas of our body have stratified squamous epithelium and other areas have simple squamous epithelium?

Since this is not my area of expertise, I searched Google under the key words "squamous epithelium, simple or stratified" to get these possible sources:

http://www.google.com/search?client=safari&rls=en&q=squamous+epithelium,+simple+or+stratified&ie=UTF-8&oe=UTF-8

In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.