I have a collection of every set of armor in the game and it's a real shame that I can only display 5 of them. Needs more mannequins. Just sayin'.

You can have mannequins in rooms other than the armoury, besides, the armoury is for storing what you will use, not just displaying your things.

The Armoury is for "Let's get dangerous" times, when you bust in, your BEST and most powerful gear laid out, ready for use. The others are more vanity.