Yup, that's actually pretty natural if there isn't an intentionally constructed system in place to prevent it. It's called a 'dialect'. They tend to develop in geographic areas relatively isolated from societal centers. It's related to how human language works.
First, there's a matter of language change - the same process behind the fact that we speak differently from the Brits and the Australians, and all three speak differently from Chaucer. (See L. Campbell's
Historical Linguistics : An Introduction for more on language change.)
Second, there's a matter of, basically, language mixing. For example, you might notice that Irish or Scottish English has a certain accent to it. Well, that's not just due to language change, it is also due to the fact that the first of their ancestors to learn English were bilingual in Celtic languages, and a little bit of influence from those languages was passed on to their children. Similar with the Minnesota area 'Yooper' accent; a lot of the qualities of that accent are things inherited from the languages spoken by the Scandinavian immigrants who came over, and learned English as a second language. Vowels in Yooper dialect, for example, involve much less tongue movement during production than vowels in mainstream American English.
The examples I mentioned are not very stark examples, but people in more isolated areas tend to have even more changes outside of the mainstream changes, and tend to retain more of the qualities of the languages their ancestors spoke before learning English.
I'm not familiar with specific examples, but supposedly a lot of dialects of English spoken by black people have a similar history; influence from the languages spoken by their ancestors and relative social isolation leading to different changes occurring in those dialects than in the mainstream dialects.
Now, I am *NOT* saying that dialects, within a single nation, which make it difficult for everyone to communicate, and which make it difficult for certain groups to participate in intellectual or public life, are something we must just happily accept.
It's important to educate people in a county in a way that enables them to all communicate with each other. This is something the educational system seems to be doing less and less well (it dealt quite well with the waves of immigrants at the turn of the last century). If anything, that means that in a nation covering a huge geographic spread, it is extra important to confront the underlying mechanics of language chance and dialects.
In my opinion, having schools which don't teach the mainstream dialect to students is a very sad way of cutting them off from mainstream culture, discussion of politics, ideas, and so on... We should know how to do it; the school system did it for for German, Italian, Russian, etc., immigrants back around 1900. My guess is, not bothering to do this is one way to keep people voting for Democrats, who thrive on others being dependent. Sad.
It's called shuckin' and jivin'. If they had talked to you, instead of each other, you could have understood them.