Ah, those things weren't done by the kind of Excel-wielding people the article talks about.
Those mistakes were done by programmers proper. With CS degress and everything.
It's not the small mom & pop or mid-sized company that usually bills people two or three times -- those knew how to bill even before excel.
More often than not, it's the multi-million enterprise crap large corporations use, with 400 options and convoluted procedures. I mean I've been double billed by the utility (electricity) company, and that's surely not due to the bill being in any Excel file.