A thought experiment

[timelets]

Imagine that due to some mysterious genetic disease, all men went extinct and only women survived, reproducing through a carefully designed gene-mixing procedure. Some of these women work as mathematicians and programmers. Since all men are long gone, a certain kind of genius lore has developed, so that all exceptionally smart mathematicians and programmers are now called "men." For example, somebody might say about a particular talented girl, "She's smart as a man" and nobody would take offense.

By contrast, if somebody said the same thing within the same "math and programming" context today a lot of people would be offended. Why is that? What's the difference?