I doubt steam needs it. I have steam on my home comp, but haven’t used it in a LONG time.
I’d say that something on your system DID need it though, and your computer has been downloading updates for it ever since.
You can try removing all of it and see if a program stops working. If not, you’re good to go.
Have a look here: http://forums.mydigitallife.info/archive/index.php/t-24588.html?s=c6f9b962b9451dfdcc7027bccff727c1