I havent been to Italy for a while, but the times I have been there, pretty much every restaurant charged a coperto. And since 60% of Argentines are of Italian descent, I am pretty sure thats where the cubierto comes from. I am told in Italy these days its 2 or 3 euros.
I have found that in the last 15 years, the number of restaurants that charge it in Buenos Aires declines every year. It used to be really common, especially for nicer restaurants. I think I have been charged it ONCE in the last few years.
So its always possible, but really rare these days.