First of all, the data center locations. I am fairly sure there is no datacenter in Redmond. Pretty much everything Microsoft hosts is hosted in California, or other data centers around the world. It is true that the server team is working on geohosting, however, I am not sure this has been put to action for WLM yet — If not, then it is still single point of failure as Peter said.

Also, the NS (Notification Server) is only a small part of the servers. You are actually missing a pretty big layer, called the Presence Servers. Also, although “Switchboard” is still the most used name, the official name of these servers are “Mixers”.

Again, nice you want to inform people, but your blog post could have done with a bit more research, and some better descriptions and explanations, and as Scott has said before, there are already pretty good explanations (by the team themselves!) in video form.