To get the skin specific fonts working in different default skins you have to do the following:
1. copy the *.ttf files from this fonts-directory to your default skins fonts dir
2. copy the content of the file Font.xml to the Font.xml file of your default skin (details are explained in the file itself)
3. restart XBMC

Unfortunately, you have to redo these steps every time you update your default skin (if you update it via XBMC addon manager).