Heh I just gave my date of birth as "1999" on another site requiring a generic profile. And, surprise surprise they think I'm a woman, too!
OK, here's an example of the output of the acs-templating form style (used with ad_form) which marks required elements with an asterisk that I wrote for Greenpeace last summer. Check it out ...
Matthew, the reason you give for not displaying the asterisk in some cases makes sense, but I think it is that rare that I would perfectly happy if the toolkit doesn't support it out of the box, but rather always shows some marker to indicate required fields.
If someone wants to be sleazy he should pay a developer to implement it, not get it for free 😉.