It is important to remember there is no "win the war" in the AvA. "Resetting" the map porks the arena until a staff member can be found to apply the proper settings again. For this reason, base captures are usually made more difficult, either through reduced down times, increased troop requirements or both.
Why leave base captures enabled at all, you ask?
The AvA is about the historic matchups and the fights. For some, this means having some type of "mission" or a goal to accomplish. Although the mechanics of a base capture are "gamey" to put it mildly, it is one mechanism that is obvious, available and easily understood by all who play the game.
In the Battle of Britain maps, groups will sometimes come together and set up a German bombing raid on London (the HQ). The purpose isn't really to take down the HQ, but rather historic flavor of a mission and the resulting fight -- can you possibly survive?
On several occasions, AvA squads have come in and done a capture mission while others have tried to deny them that. The base itself wasn't so much the goal as finding out "do we have the skill to pull it off." It's the same theory as the bombing London scenario, only using a different mechanism.
I hope that helps.
