There really is no "normal" wide or narrow stance. Much of one's stance width depends on one's height and body build, (taller people with bigger bodies can typically go wider then shorter people with smaller bodies). Ultimately though, it's mainly just comfort. There are benefits and disadvantages of both narrow and wide, so if you think wide stance suits your riding style better, find what feels the most comfortable for you within that dimension. I think a wide-stance can be classified as above 19.5in, but it really depends on the person.
I typically wouldn't just put my bindings are wide as they go for park, because while you do gain more stability and board flex, going to wide can be detrimental overall. If riding that wide doesn't bother you though, it might not be a problem.
PowderHound and TreeNinja