Don't be foolish. All the wiki article shows is that it's recognized as a variant by some and not by others.
"Ain't" was considered incorrect for a long time too. Common usage caused it to be accepted eventually. That's how it works with language, since language is not static but ever evolving. So stop imagining that the way YOU like it is the only way it should be.
Ain't is still incorrect.... Now I just need to figure out why Firefox isn't underlining it, LIKE IT SHOULD BE.