Using drivers as a modules have some interesting effect for embedded devices. They allow the kernel to boot speedier, reduce the size of kernel, allow you to fine tune the memory footprint (by inserting only usefull modules and removing the non useful one) etc...
Even if that sound strange for some, the kernel modularity have some usefullness even on embedded programming (for thoses who are insterested I recommand this website :
http://elinux.org/Main_Page )
And for installing the PocketBook firmware on the opus, you have another choice: working for Bookeen or for PocketBook, you may have access to some informations that are not publicly available
