“We removed these sound events for performance reasons. We pay a lot of attention to how quickly the machine powers on, powers off, goes to sleep, resumes from sleep, etc.  As part of speeding this up, we experiment a lot with what process is in control of the startup and shutdown sounds. In an interim build of Windows 8 while it was under development, we were able to speed things up considerably by moving the shutdown sound from Explorer.exe (which is running while you’re still logged on) to Logonui.exe (which is the process that shows the "Shutting down" circle.)

However, moving the shutdown sound this late started running into other problems. The code we use to play the sound (the PlaySound API) needs to read from the registry (to see what the preferences for this sound were) and from the disk (to read the .wav file), and we ran into issues where the sound was unable to play (or got cut off halfway) because we had shut down the registry or the disk already!  We could have spent time rewriting the API but we decided the safest and most performant thing to do was to eliminate the sound altogether.”