Nope. Purchasing updates is for every update. Anyway, it's easier for us to give the final version of the game to patrons, because we can easily see the lifetime support of that patron. Even if you just pledge when there's a release of the game, for us it's easier later to give discount or other rewards.
And it's not weird you share this with us. We really like hearing stuff from this. We like to thing that our games can give something more besides the adult content.