Yes, the articles, web pages, calculators etc (if there are any other things) referring to the Grecian Ideal are based on classical sculptures. Not always actually Greek sculptures: the statue of David is by Michelangelo, and there may be other exceptions.
Undoubtedly if high level competitive natural bb'ers, and let's say ones that generally were thought to be more aesthetic, were measured the ratios would be somewhat different.
Not really so drastically though.
The thing about it being ratios is that while the modern bodybuilder may be larger in each measurement, that doesn't mean the proportions have to be greatly different.
That said, though, the modern bb'ing ideal of leg size is somewhat larger relative to upper body size than the "Grecian Ideal" proportion.
One way that this has been put is that the classical ideal, and what bb'ing a while back was looking for, was the V-frame shape whereas now the bb'ing ideal is the X-frame.
However, for someone who would ask about these proportions rather than simply aiming to improve as much as possible everywhere that is possible, I think they would be unlikely to be unhappy with obtaining proportions similar to the Greek Ideal provided that the sizes involved are all decent.
(Obviously, there's no use in everything being proportional, but the arms being 12", the legs 18", etc.)