I was not sure if this has been confirmed but... the OS X "new version" web page at Apple UK now reads:
Mac OS X version 10.1 will ship this September and will be available as a full retail package through the Apple Store and Apple Authorised Resellers for a suggested selling price of �99 (inc VAT). An upgrade CD will be available to current Mac OS X users through the Mac OS Up-To-Date programme for a shipping and handling fee of �15.
So that kinda confirms the whole "$20 = Update CD" Apologies if this was already confirmed.