i really don't think steam can handle what will happen. Everytime a CS patch has come out it crashes.
We all know there are a shitload of CS players, but lets add in all the people that hate CS and are just waiting for a new game. I think there are 10-15x the amount of gamers in the second catagory. If the CS players alone can crash steam I think their servers will melt upon the HL2 release.