As I understood Scott's explanation, the reason is that if he were to make any future changes in format, style or layout, he would have to do it twice: once for the six styles you can see (which are all derivatives of the new default), and the second time for the standard "classic" xenforo style which is totally independent of the new styles.I read that earlier - not sure why it couldn't be installed as an independent theme.
Is there a way to change the default fonts in the threads to be something a little more modern?
Ok I did pick a different font in AD Styler. It only changed the font at the bottom blue.