Email is just as much a strawman. Compare how simple email is to all of the features Facebook provides (and don't forget your ability to click on your cows in Farmville).
You say there are no technical reasons why it can't work. That is very akin to the "You can do anything, it's just a simple matter of coding." The reality is that some problems become intractable due to their complexity. Distributed social network may not be intractable (Diaspora will probably figure that out), but it's a hell of a lot harder than email.
Just to clarify, when I said 'technical reason' I meant from the perspective of a user being able to setup/configure their social network settings. Not from the perspective of the internal implementation of the server components
You say there are no technical reasons why it can't work. That is very akin to the "You can do anything, it's just a simple matter of coding." The reality is that some problems become intractable due to their complexity. Distributed social network may not be intractable (Diaspora will probably figure that out), but it's a hell of a lot harder than email.