Good comment from Nilda.
As I'm sure you know, Nilda is not the first person to disagree with McLuhan's thoughts on TV! He tends to use wide, sweeping statements to counter the common knowledge that TV is bad. I guess the theory is "if only 1 person is saying it, you better say it big."
I never read Ursula Le Guin, but I would think most people agree with her. But keep mind that she is a writer. TV has whittled away to influence of her chosen profession. She most likely has an inherent bias against TV. If she were a TV news broadcaster, she may have a different opinion! Likewise, I'm sure Monet would have had something against the camera. So while I respect her comments, I do take them with a grain of salt.
McLuhan's idea is that TV engages you. It moves in front on you and you have to keep up with it. That is the active part. Printed materials are static, non-moving. They just sit there, waiting for you to engage them on their terms. This was confusing to me at first, because if TV does all the work for you, then it is passive. And if reading needs you to act, then it should be called an active medium, right?!?
No, that is not McLuhan's argument. For him, the medium itself trumps the content ("the medium is the message"). So how the TV communicates itself is what matters, which is why TV is more active. He goes on and on about it, and I recommend reading his Playboy interview. It gets all his major concepts across without the painful verbosity of his more academic work. I would summarize, but that's a blog post I don't have the patience to write.