You're right, Blizzard is another one of those companies. I forgot about them.
What I really like about Valve is that they don't leave the high-end users "high and dry" so to speak. They give players a wide range of options. You can play without HDR lighting, without dynamic shadows, without high quality reflections, without all that stuff on your low-end system, and it will still look good and run at a high framerate. Or if you have that SLI setup, you can crank everything up until your eyes bleed. It takes a lot these days to convince me to upgrade my PC. I'm glad I can enjoy TF2 without having to do so, but I'm also glad that when I eventually do upgrade, TF2 will look even better.