Hi jamie, think this is one for you - hopefully i'll have a patch for you to review!
(And, sorry i've left it so late to report this - I was aware of changes to this, and there are now problems...)
There is a image of a red asterisk in the <label> against required form fields, but it is hidden with:
Issue 1 is that display:none means "expunge me from the DOM tree" and for some browser/ screen-reader combinations this means don't speak me. The work around is illustrated by the Standard theme class 'accesshide':
So, that's one way to fix it BUT issue 2 is that the only visible cue is dark red text in a <label> for a required field - if you're colour blind this may appear black, if you override with high-contrast settings...etc. - basic accessibility says do not convey information with colour alone.
So I propose we show the red asterisk icon, perhaps add a title and help cursor, and keep the red text if you wish.