Flattr's blog post seems to have a bit of that "not fair!" tone to it, which they - for better or for worse - don't actually have the right to say.

I can definitely see the argument from Twitter's side, even if I don't agree with it. But more than that: these are Twitter's terms! You can't roll in and start arguing for benefit-of-the-doubt with the people that wrote the terms for their own platform.

If you build your app on another company's platform to monetize their platform and they decide you can't, you're just falling into a trap you set for yourself. Even if it would be cooler if they allowed it.