I agree with your analysis, but it's worth noting that size/scale aren't everything. Hacker News isn't the size of Reddit (or Digg at its height) and I'm kind of glad about that.
If App.Net ends up being the 'Hacker News Twitterlike' service, is that a success or failure?
The difference is that Hacker News doesn't need to turn a profit. app.net has a number of running costs that need to be serviced and, to do that, people have to want to pay. There is a minimum threshold that is required to keep users with the service, otherwise it feels empty.
Examples are Google Wave vs Google+. The former felt empty and pointless, while the latter can be interesting because of the number of users, albeit they may not be people you know.
It's not a good example though, because no one knew what the hell to use Wave for anyway. It was just a conglomeration of product features that had no clear place to fit into existing workflows.
Twitter on the other hand fits in everywhere. People just love to crap out little 160 character nuggets in between everything else they do all day long.
Is it such a bad example? I'm not sure what app.net is. A "real-time social feed" that I pay for? As a developer (his primary audience), what does this do for me over Twitter or Facebook?
If App.Net ends up being the 'Hacker News Twitterlike' service, is that a success or failure?