1. AL_DISPLAY isn't quite the same as AL_BITMAP. 2. AL_DISPLAY is not what generates input events. Probably we need some kinda' struct like AL_SYSTEM (AL_SYSTEM_WIN32 might be a particular implementation of it) which will store the HWND. A user might create a window (which is not rendered thru' Allegro), however, he might be able to get input events from it).
3. Seperation of AL_DISPLAY and AL_BITMAP can make it possible to create off screen surfaces, multiple targets which can simplify coding the graphics subsystem. 4. AL_SURFACE is a generic surface on which a variety of functions can be performed. Blitting is just one of them. Let's say AL_BITMAP is a regular version of AL_SURFACE. (Poll: Does anybody oppose this?)