I see this all the time. Fortunately I started out working for a utility and am aware of their excellent historical billing records. They rarely miss. And as said by others, it they do, they make if good and replace with a larger service.
Yet, I still grouse about the excessively conservative demand factors in the NEC. There have been several projects I really had to sharpen my pencil to have a reasonable sized service, but I sure didn't cut things so short I would be libel for an undersized service. That would cost serious $$$!
It's my name going on that drawing, not yours. If what you want ain't right, it ain't going on the drawings!