If the .io guys send out attack lawyers, it will be the biggest waste of time and money ever for a startup.
Neither of these services have any traction, and TwitVid is a mediocre name anyway (it's way too derivative of TwitPic). So what prize would they be fighting over?
And while they're busy consulting with lawyers, someone somewhere will launch TwitTube / YouTwit / Twideo and kick their asses.
I hope twitvid.com finds out they are wrong.