http://www.whatwg.org/specs/web-apps/current-work/multipage/...
From the looks of it - while just about legal, it's the worst option going. <em> etc are far more preferable and 'right'
I don't consider my bolds and italics to be mere style and much less I consider them mere suggestions.
Bold and italic are typographic conventions of author _intent_ (that is: semantics) with centuries of use. I put them there in purpose, and I don't want them converted to anything else via styling. Sure, someone can style "b" as "purple text with a yellow dotted underline", but I might as well make my _actual_ intention clear.
Outside of its proper context, "semantic" is just a BS notion that got popular with designers and co because it sounds sophisticated, giving rise to inane arguments similar to how many angels fit in the head of a needle.
I'm happy when they don't use idiotic alt tags. If they manage to use good alt tags I'm really happy.
Accessible web design is seen as some freakish niche need, and is often relegated to something to do later, if ever.
Although, I think modern terminals can do bold fonts, e.g this gives you bold in bash:
echo -e "\033[1mtest\033[0m again"