ISO, and many places, yes, but not everywhere. Is it necessary to add "At least in the civilized world"? Seems unnecessarily inflammatory. And the gp is proposing a new system anyway.
The point was that the proposal is based on assumptions that don't hold true in ever culture, but would be forced onto those cultures if it were implemented. This is of course true for most, if not all, proposals for changing the way we handle time.
According to Wikipedia there are at least three "first day of the week" in use, sorted by (my assumption of) affected population:
Monday: EU and most of other European countries, most of Asia and Oceania
Sunday: Canada, USA, Korea, Japan, Israel, South Africa, most of Latin America
Wikipedia says the first day of the week in New Zealand is Monday, but our calendars usually start on Sunday and personally at least, I've always thought of Sunday as the first day of the week. So I'm not sure I'd trust that page too well.
It's really not important at all... The point is this calendar would line up the week cycle with the month cycle, which has a ton of advantages. You can't throw that away just because you can't agree what day of the week should come first.
Hell, while we are at it we can just rename the days firstday, secondday, etc, and not have to deal with that issue.