This should instead be be <strong></strong> and <em></em> tags to follow the HTML 5 specs.
Also there's 2 HTML 5 tag for strike-through: <del></del> and <s></s>. The last one also seems to be missing in WeBuilders HTML def.
Note: According to the HTML 5 specification, the <b> tag should be used as a LAST resort when no other tag is more appropriate. The HTML 5 specification states that headings should be denoted with the <h1> to <h6> tags, emphasized text should be denoted with the <em> tag, important text should be denoted with the <strong> tag, and marked/highlighted text should use the <mark> tag.