Do you mean the mentioned items in the main, or new mail window?
If the former, I believe the MS thinking on this is, if you wished to use the normal (in) window, then there would need to be something worth using, as you are already composing a new email in another windw.(Hope that makes sense?)
However, following this idea, if, for example you have mail in your inbox, or, for example, your deleted box, and click it, the main window will become active again.
It follows, I hope, that if you have nothing in those boxes then, there being no required action, the interactive menus stay greyed.
But (I just checked to be sure!) I have not experienced this when replying.
fwiw. Confirm you are using the latest (2011)?