According to Jeff Grubb at his video around the 20 minutes mark We've Been Using the Steam Controller! | Giant Bomb Review Discussion the Steam Controller will work as a regular controller without Steam being open. Steam itself is not required to use the controller, it just adds additional non standard features when open, such as customization and gyro. Sounds like without Steam being open it acts similar to a Xbox controller. But for that case there would be no need to pay 100 Dollar / Euro.

I wish though there was a more universal driver and software to that can be installed to run in the background, without Steam. So I agree with your sentiment, but just wanted mention that the controller is still (partially) functional without Steam. My suggestion is to buy the Steam Controller only, if you want to use it with Steam (duh!).