Two days back I added Paperwhite to my good old Kindle 3 - and ran into this issue.
I embedded full font family (four files) into epub using Calibre plugin
from our forum. I just tweaked this plugin a bit so that element body{font-family: Font_Family_Name;} was written into epub's css (without this tweak K3 did not display embedded font).
Bottom line: Converted file allowed switch between Helvetica and embedded CharisSIL on K3.
Well, copied azw3 to PW: Surprise, switch to Publisher font did nothing!
Why?
I tried to use Kindlegen 2.8 for epub->mobi conversion, same effect: Publisher font works on K3, pulisher font fails on PW.
I uploaded example
here. This is a free epub book by G K Chesterton downloaded from mobileread. In this example epub with trailing undescores contains embedded font, mobi was obtained by Kindlegen 2.8, azw3 is Calibre output.
Maybe someone can give me a hint why I cannot switch to publisher font on PW?