1. Why are we having people sign up on the website?

There are several reasons.
- Allow people to become an official member of the PSF (just requires agreeing to the code of conduct, but that requires at least some minimal infrastructure)
- Create an opt-in list of Pythonistas
- Allow (over time) better connections between Pythonistas that have similar interests or are in a particular location
- Allow people to be granted editing privileges on the website
- Allow people to manage membership levels
None of these are necessary, and if anyone is under the impression that signing up is required to learn or use Python, that is incorrect. We are trying to build a completely opt-in set of services that will help people in the Python community connect with each other. Steve's suggestion about having the edu-sig be served by the website is right on, and part of what we are working toward. 
2. Why are we doing this?

The PSF's only mission is to support Python and the Python community.  We have found that it is very hard to provide structured support to community activities when we don't have any way of reaching out and communicating with people in the community. For example, a couple of years ago we wanted to find out everything we could about the use of Python in Europe. We had to just put out a call on the blog... and hope. This is suboptimal. If people want nothing to do with it, no problem.