^ Thats because (technically), when you place a battallion into a structure in the normal game, you dont actually garrison it - you gain ownership of it instead, and in doing so the structure just has a normal (bow) weapon.
In my 'extended edition' (sic) you get to garrison structures properly, meaning that not only will such structures gain a fire arrow weapon when you have upgraded your archers, but you can also remove battallions from them and continue to use them too

This means that its now actually worth building Battle Towers and such as you can now load them up with stronger troops (Sentry Towers stay as they were) - in the normal game they are just a more expensive version of Sentry Towers.
And I can tell you, its a bitch to get the whole thing working properly - not as easy as you may think.
More info here, should be done in couple of days;-
http://www.deezire.net/modules.php?n...ewtopic&t=9791