I don't think the launch of the Nextbox is going to be bad like people think.
MS has run XBL very well over the years. They also run tons of other services that are used by millions of people (Outlook, Office365, Skype / Messenger, Xbox Music/Video, App store, etc etc). Halo 4 also uses Azure for its services in the backend (there's videos on Channel9 talking about this, it's highly scalable depending on load), and they didn't crash when Halo launched.
They know how to create a service that scales. Nothing is perfect, you can of course point to various outages XBL has had over the years. The Xmas of 07 was the worst by far. No company has a perfect track record. Even Google / Gmail have gone out over the course of years.
For third-party games though, it might be a different story. Most companies just don't have the expertise in launching large services. We can only hope the devs do their jobs right, and take the right measures to make sure we don't have Diablo3 or Sim City-esque catastrophes on launch day. I'm actually slightly worried about Destiny's launch for example. That's going to be a lot of people form tons of different platforms hitting their servers. We'll see though.