anweis,
You are correct that for years we did manipulate habitats for game production, often to the detriment of the game in question or the longevity of the habitat itself. Man made infrastructure and invasive species were created and brought in that forever changed the movement, watering and feeding patterns of wildlife (yes, even birds) out of traditional migration patterns. 50-100 years ago, what we thought was a good thing for the habitat or necessary for the economy turned out to be exactly the opposite.
The trend now is to teach future resource managers to maintain and preserve what natural habitat is left, improve the connectivity between the fragmented portions of the habitat increasing the useability for the game to be managed, and if possible (and if needed) to begin to restore damaged or altered habitat/landscapes to a realistic previous point in time where the habitat and the wildlife therein are a sustainable, perpetuating resource.
Having the absolute maximum number of animals in a given habitat so that you can shoot more isn't good management strategy. Generally, they will end up eating themselves out of house and home, and the population will ultimately crash, taking the genetic resource that delivered that giant buck away. That is not just my opinion, but a well documented experience in ungulate management.