Same goes for reserve bandwidth, etc. If they did this every time there were capacity issues, they'd quickly overcome them. Doubling might sound like a lot, but valve has humongous growth rates anyway, they'd need that capacity pretty soon regardless.
You keep using Steam despite having supposedly many issues with it. Why should they change anything? You act like this stuff is a big deal but you don't do anything about it. I can't say your attitude about their problems being easy to solve by just throwing money at them is very realistic or knowledgeable either. Valve doesn't have their own dedicated worldwide network in a traditional sense, they peer with major hubs around the world using CDN placement. They can't just magically make all of the peers be able to handle their capacity either. It's amazing it stays up at all under the weight of 20 million users mashing at the same time to see what the sales are while also delivering patches, demos, streaming video and all that shit.
If it's so insufferable then start exploring the problem with Steam Support or stop using it. I can't think of a single service other than Amazon that manages to handle that kind of burst demand without investing hundreds of millions into infrastructure. Maybe Valve does need to investigate more distributed load balancing like Amazon but don't act like that's going to happen quickly, without growing pains or affecting things people like about Steam like the frequent sales.