I have no idea why @jaizei 's birthday doesn't show up under "Today's Birthdays" on the member page, but it doesn't. So I DO have a good excuse for missing it this a.m.
So here's cake in your face, Cameron - my favorite moderator!!
I think the birthday box on the members page follows the permissions from the members profile settings. If member has birthday set to not show on profile, it won't show on the member page. The birthday banners are separate and don't seem to follow that privacy setting. I think theres also an activity trigger for the banner to display; your account has to be active that day for the banner to show.