Hope not to butt in too aggressively here.
i think the money part is obviously very important. This has been observed even when games where a far cry from the kind of business they are now, and even if games were not so widely lauded as art as they are today, they were at the same time not simply considered "products" to shell out each year as much either.
So for profits, the server model is probably not only about anti-piracy, but about selling "new" products continuously, and Ross mentioned some things in the video that do show this kind of "selling then breaking the games" might have something to do with it, for example when he relayed that it will take a week or so for the developers to make a game ready for long term enjoyment, just like we would hope for games or (non-live) art to be.
So the time and money involved is not too significant (and worth it, if the proud developers are trying to preserve an evergreen..) . It would also not affect the company's income in any way as they have stopped to sell the game at this point any way, it is "dead". Only that, were it still alive, fewer people would buy the next game that is exactly the same but with updated graphics.
By the way some people still play Tribes 1, it is possible to download for free, only most servers are in the US. Great game, but sadly people have wandered off to the sequels