I just had a small “a-hah”.
But as they pointed out in the twitter bootstrap documentation, <b> and <i> are still valid!
Most people seem to think they were deprecated because they have no semantic meaning – that was certainly my impression.
But they were not deprecated – in fact they were kept around for the very same reason – because they have no semantic meaning.
In other words, if you need to highlight words of phrases without conveying additional importance, you should be using <b>, while <i> can be used for example to stress technical terms or voice, again, without communicating anything semantic, just for visual distinction.
This may seem like a tiny, irrelevant thing, but I find these details can be helpful when thinking about HTML as a “rich text” medium.