Re: Capturing archer towers
You are not missing something, it has been changed. You can no longer capture any part of a castle or city except the gates themselves. Note that this does not include the gatehouse towers. All city and castle towers will continue to fire arrows while any friendly unit is nearby. If you want to silence the towers, you need to kill or run off any nearby enemy unit. Even after that is done, there is no possible way to gain control of the towers yourself and have them fire at the defenders.
The upside of this is that towers on an undefended section of wall will not fire at you. So, a city defended by one unit of peasants can no longer burn siege towers attacking multiple gates.
Re: Capturing archer towers
This is in the manual, but I don't know if it's correct. According to the manual, the towers fire for the owner of the settlement providing one of that owner's units is nearby. You can take control of the square while troops are still on the walls. If that bit in the manual is correct, taking the square will suddenly cause all towers to belong to you, and any near your units will begin firing on enemy units within line of sight and range. It's pg. 58 in the manual, under Using Defensive Fortifications.
Re: Capturing archer towers
Too see how it works, go into a custom battle or wait for one in the campaign and move your men around the fortifications during deployment, you'll see a flag pop out of the tower showing it is activated The tower gates will always be active as long as you have 1 unit within a certain distance of the gatehouse but as the defender you have to control both the top of the gatehouse and behind it, the attacker only has to capture 1 to gain control. Also a routing/fighting to the death unit will cause the owner to lose control of the tower.