In order to use the <b> tag within html text in flash and have Flash automatically detect the right font to use for bold, you must embed both character sets and specify the fontWeight of both.
Sounds more complicated than it is. Just use the following code when embedding fonts:
[Embed(mimeType='application/x-font', source='fonts/myFont-Medium.ttf', fontName='myfont')]
private var font:Class;
private var font:Class;
[Embed(mimeType='application/x-font', source='fonts/myFont-Bold.ttf', fontName='myfont', fontWeight='bold')]
private var fontBold:Class;
