I think Rosetti is supposed to be injecting a feel of the "real" movie-style Sicilian gangster people expect to see. Up to this point, everyone has either been posh and sophisticated, or just low-brow blue-collarish. The closest was Horvitz, but he was really just somewhere between those two. The one character expected to be more like Rosetti so far hasn't been; Al Capone.
So, yeah, I think that's the entire point of his character. To give us a more Joe Pesci kinda guy to satisfy people's expectations of what a mobster is.