remote button wake is easy to test. Just connect your remote button and push (or connect the cam usb cable) when the camera is off. If that cam support wakeup it will... wake up. It is actually is not a CHDK function, it is canon's own usb function, turning on the camera when you connect the usb cable to your pc. Then CHDK kick in and run the remote script if script autoload is enabled etc.
Ah, thanks fingalo, that clears things up quite a bit
I couldn't get my a570is (1.00e) to start up by plugging the usb cable. I tried in play mode and in rec mode in M/P/AUTO shooting modes just in case they had anything to do with this but nothing worked. Also, gphoto2 can't connect to the camera via USB until I power the camera on myself and lsusb (on Linux) won't list the camera until it's powered on either. I didn't test with an external power supply connected, but I'm guessing it wouldn't help.
The a570is doesn't support remote capture, maybe the USB startup feature is linked to it in Canon's typical feature list?
Anyway, it's possible to switch the camera on using a solenoid or some other mechanical actuator, without having to take the camera apart. That's quite kludgy, of course.