em and strong are not announced by screen readers

Semantic HTML is the foundation of accessible websites. Meaningful HTML elements enable assistive technology to transform a site's information into a different form or shape. A screen reader, for example, takes a site and reads it out for the visitor. Semantic HTML keeps your content and information accessible.

And yet, here I am after all these years of advocating for using strong (strong importance, seriousness, or urgency) and em (stress emphasis) instead of b (bold) and i (idiomatic text – italic), only to learn that screen readers don't announce strong or em.

I'm not a daily screen reader user, and VoiceOver isn't the only one out there, but a quick test on my Mac proves the fact.

Martin Underhill shares more resources on his blog if you want to learn more.

Edit: Steve Faulkner shared that some screen readers have a "style reporting" option which can convey additional information. This setting is far off the default, though.