Now I'm sure having to cater to the advertisers certainly affects the decision making(even a bit adversely at times), however their massive following is essentially what makes them valuable.
I also notice that whenever this idea is challenged, I only see people simply parroting his belabored battle-cry of "catering to the users" without actually giving any concrete examples. I'm not against app.net's idea, I just believe the true novelty of this project is creating a micro-twitter(which can also be created on twitter by simply following certain people) for affluent tech people, and _keeping_ it that way via the subscription fee.
Besides that, I haven't read or heard of anything that they plan to do fundamentally different than twitter. Honestly, even if they do, and it actually proves to be a great feature that users love, I don't see why twitter can't simply copy it and perhaps even make it better.