I've looked into this in depth. As of now, logon, logoff and certain other sounds are not in the Windows 8 CP sound scheme. That might be due to the fact logging off is signing off and such. Also, the startup sound from the era of Windows vista and 7 is disabled by default, but still plays when enabled when the PC is restarted and sometimes resuming from shut down. It's changeable though. Also, the other sound schemes from 7, they're not in the sounds list, BUT the audio files are still there in the Media folder under the Windows folder in the C drive. There is also a new sound I haven't been able to locate, it's a metro sound. It's kind of a twinkle that sounds like a mix from the Aero design of vista and 7 but metroie like 8 is.
To me, this suggests that AT LAST, there will be a new sound scheme!!!
Microsoft seems to have left the very core default sound events enabled, but some are not there. Also, the startup sound is disabled by default as since metro design is not Aero design like 7 and vista.
I AM SO EXCITED!! Literally, one of the major things I've wanted with Windows 8 is to have a new sound scheme. We've been using the same one since vista, for SIX YEARS! No more! But right now, I've swapped those sounds out with my own sound scheme. So yeah.