I cannot think of a single other game company that would even think of updating something this old.
Counter-Strike 1.6 is an active product that is still sold and is still the most popular FPS on the market. Valve have plenty of good reasons to continue to update the engine. Compare 10k+ CS 1.6 players (didn't it used to be in the 70-80K range on Gamespy Stats?) to around 1,000 for UT99, and that's the reason Epic isn't fixing exploits.
Additionally, Starcraft is still patched (for the same reason), and was released in 1998. id released a patch for Quake3 post-GPL to fix some security issues last year, which came out in 1999.
While I'm glad that Valve support their games, acting like it's done out of the goodwill of Valve's heart is ignoring the reality of the situation.
This comment was edited on Oct 23, 2008, 17:06.