If I click on the item's gear icon on the File List for the contextual menu, I get access to the Services menu.
If I invoke the contextual menu via the keyboard shortcut, the Services menu is not there.
Oh, that's an interesting observation. I haven't noticed this before.
It's probably related to how Services menu is added by the system automatically.
I'll have a look if it's possible to add Services to the keyboard menu invocation. Or perhaps trick the system into adding it.