I thinks all this is because of the majority of us, the KF community, who dont care about the graphics but the gameplay and will enjoy this game for a long long time. Many kids will quit because KF is not Crysis 2 in visuals but who cares about them. So TWI simply see that the KF players play the game no matter what and they decide to support it.
Every TWI game that I purchased is a long time investment because I know It will stay alive for a long time. Not like CoD - every year new game instead of just add the new content to the last one (since every CoD runs the same lame engine lol).