If this has been common knowledge for so long why haven't Cessna corrected it? Doesn't fill you with confidence does it. I work in pounds so it doesn't really affect me but it makes you wonder what other errors there are in there (and indeed in other POH's).
The whole area of weight and balance and performance charts is a bit of a 'plus and minus 20%' game to me. (Yes I'm aware of the CAA performance multipliers.)