this has just begun to happen to me and i dont think its natural.
in the past, if i were say using my powerbook g4 downstairs, closed the lid for sleeping while i went back upstairs and reconnected the system, it would wake up upon reattaching of usb peripherals like my external hub for kb, mouse, etc.
but now, i am experiencing this too. i put the computer there and reconnect cables and it wont wake up. i have to reboot, thus losing unsaved work.
i seriously dont think this is jsut one of those "thats the way it is, too bad, the mac is built that way" issues because it didnt use to happen but now it does. any help would be appreciated