In Device Manager you can configure any USB device to not wake the computer (“Allow This Device to Wake the Computer”). I usually do this for mice.

> why is the only way to send Windows to sleep a four-key combination (win+x,u,s)

Using OpenShell, the slightly shorter Win-Right-Return works for me. Some keyboards used to have a dedicated off/sleep/suspend key. You can map any shortcut you like using AutoHotKey, or you can bind a global keyboard shortcut to a batch file via a file shortcut in the start menu (Ctrl+Alt+something), or by pinning it to the task bar (Win-n).