They've probably had to spend plenty of hours waiting in line while cashiers chatted with the patrons in front of them, so once again, you're more or less.
A year or two ago I was trying to check some books or movies out of my local library. The librarian was chatting -- she had a pronounced Southern accent -- with the patron in front of me for what felt like a good long time.
Finally, the patron took her items and moved away from the desk. I pushed my items across the counter to the librarian, expecting them to be checked out.
The librarian goes on talking to the patron for a while longer, and when she finally checks out my items she says, "That was so rude! I was talking to her. Do you know how rude you were?!"
I wanted to say something, but figured I'd better let it go. I couldn't think of anything on the spur of the moment anyway.
Looking back, maybe it has to do with multi-tasking. A librarian or store clerk or cashier in the North might want to carry on a long conversation with a friend or coworker (if they were young and undisciplined enough), but she or he would probably be able to take care of another patron while this was going on.
The librarian in my case, probably thought she was being kindly and devoting her whole attention to one patron, even if it meant inconveniencing people in back and making them wait longer than they had to.
Anyway, if you think Northerners are rude or pushy, consider what they may have to put up with if they've moved South.
Then stay the hell out of the South in the first place.