That type of thing can be dependent on the region. I'm from the Northeast, where nobody but nobody calls their grandmother MeeMaw, but once I moved to the South I heard MeeMaw fairly frequently.
Poppy is common enough in the US to be included in a list of "traditional grandfather names" that I found on Grandparents.com. Along with Pop and PopPop. My sister's grandchildren call her husband, who is actually their step-grandfather, PopPop.