Yes they changed the hotkey. Officially it is now Ctrl+shift+LMB. In 4.0 alt+LMB also works. I don’t know if they’ll remove the alt+LMB in 4.1 or not. Ctrl+shift+LMB was supposed to be for people who use emulate MMB (middle mouse button), but testers seem to like it even when that option in preferences isn’t checked. Since Ctrl is used for invert brush on the other paint modes the changes weight paint to match. So now Ctrl+LMB invert weight paint instead of selecting a bone.