I (desktop PC) find the same, they are not case sensitive.
Hmmm… Perhaps that’s the way things work on a Mac?
Time to tug at @jbacus sleeve for clarification…
Update:
Reading the manual, neither Mac nor Windows documentation mention KB shortcut case sensitivity.
Assigning keyboard shortcuts (Microsoft Windows) — SketchUp Help
Assigning keyboard shortcuts (Mac OS X) — SketchUp Help