Good old truetype fonts are subsetted, but not Opentype (CFF) fonts.
Example:
++
Thomas
Example:
$~ cat foo.html
<html>
<body>
<p style="font-family:ITC New Baskerville Std">Baskerville</p>
<p style="font-family:Droid Serif">Droid Serif</p>
</body>
</html>
$~ prince foo.html
$~ pdffonts foo.pdf # mind the "sub" (subset) field
name type emb sub uni object ID
------------------------ ---------- --- --- --- ---------
NewBaskervilleStd-Roman Type 1C yes no no 4 0
PXAAAB+DroidSerif TrueType yes yes no 5 0
++
Thomas