I think this is a big part of it. As a woman I prefer handshakes in most business situations, but I would be totally fine with a hug or hug+cheek-kiss in a more casual business environment if they were also hugging/cheek-kissing my male colleagues. If they hug/cheek-kiss everybody, they're just a huggy, kissy person and that's fine. If someone hugged/kissed me but shook hands with my male colleagues, to me that says they think their relationship with me is somehow different from their relationship with my male counterparts, and that would make me very nervous.

Your "would you get coffee with no business interests" test is a neat way to think about it. Thanks! I know I definitely would hug my best friends, but would not hug my coworkers.

In a sense, it's like the German distinction between friends and acquaintances: friends are a rare treasure, whereas in America we seem to consider just about everyone friends.