I disagree. If it works, the reason non-developers will join in large numbers will have to do with the services/offerings running atop app.net. I'm in no position to guess what they'll be, but I believe they can and will be developed. And I wouldn't rule out services/bundles that include app.net membership as part of the price. There's a ton of room for innovation.
In the end, people will pay for app.net for quality and for access: ala HBO, satellite radio, etc.