I don't know, isn't that confusing sometimes? I know that I hate those menus with greyed out items and no explanation why a certain option is not available at the moment. Not even seeing the option at all might be even more confusing, because then I might start looking everywhere for the option to show up.
I don't know why we still don't have interfaces where you can always access a precise, clear, context-sensitive explanation for why a control is grayed out and when it's enabled. The benefits to usability would be huge!
