Took me a minute of googling to be vaguely sure you meant what I think you mean: the comma marking the end of your dependant interjectory clause there?

at least in America**,**

If so: I have no idea what you are talking about, that's drilled into us in school. Maybe people get lazy on the Internet but it is part of the rules and gets taught and used here

If I've misunderstood: what are you talking about, then?

I’m a comma-crazed Burgerstani, and I use those as well as the serial comma.