As they view it, it's not an unnecessary barrier. It's there for a few specific reasons: 1) Make sure there is enough interest to get the site going. 2) Build up momentum for the grand opening.

Don't forget, all these Stack Exchange sites are thought up by the community, but then deployed and paid for by Stack Exchange. They don't want hundreds of "ghost towns" around the web, they want to only create a new site if they think there's a reasonable chance it will grow into a site as vibrant as Stack Overflow. That's what the whole process is about. Time will tell if it's a good process.