Just like the English Grandma, Grandmom, Mom-Mom, Nana, Mee-Maw, etc., Polish has several diminutives for Babka (Grandmother). I called my Polish grandmother Babcia. I've also heard of folks referring to their grandmothers as Babci, Busia, Babusia, Babunia, Buśka, etc. It's probably a matter of copying whatever version your own mother used (or possibly a matter of chosing a different version than the "other" grandmother) more than a matter of being regional.
See this page: http://en.allexperts.com/q/Polish-Language-3388/babcia-dziad...