Hi Kovid, have you tried your example?
If I convert the following snippet, I get three lines which look correct in a web browser, but all three lines look identical on my Reader.
Code:
<html>
<head><title>Font test</title></head>
<body>
<p style="font-family:serif">The quick brown fox 012345</p>
<p style="font-family:sansserif">The quick brown fox 012345</p>
<p style="font-family:monospace">The quick brown fox 012345</p>
</body>
</html>