Wait! It is variable. The Developer tab requires the separation, but the others all seem to work with Alt+, as do the QAT commands.

The shortcut key display in the ribbon is just that: a display, which shows what is happening. It doesn't change the keyboard's behavior, or have any effect that requires a change in the keyboard's behavior.

When I was trying to figure out how to deal with Windows 7's misbehavior (which I thought was due to Word), I learned that I could watch the ribbon to see whether the Alt keypress had been recognized or not. But that gave me no insight into why it was being ignored sometimes and accepted sometimes.