I think he was just commenting on the factual nature of the series - not necessarily a major concern in a work of fiction. Just to remind you that there is a considerable amount of drudgery that Weinstein understandably skips in his portrayal of the day-to-day workings of a big agency. Just like he skips a few basics in character and story development!
Saatchi worked as a copywriter from some time around the early 60s and visited the US then. Even by then the big ad agencies were pretty much international (like the kind Draper works for) so basic work routines would be much the same. Madison Avenue sets the template, others comply. I seem to remember episodes from an earlier series when there are British ad men involved as well, significently.