Yup, the booklet version is fullscreen which means it doesn't have the menubar that the Kindlet inherited from the reader framework (which is itself a booklet, that opens books and Active Content and homescreen views and stuff).
Fullscreen means more space for KUAL buttons
this is supposed to be an advantage.
So you will have to use the KUAL quit button, or the KT's physical home button if you have a KT.