Joel Johnson has a couple of posts on Gizmode under the tag #takebacktakeoff in which he rants a bit about our rights to use our gadgets on airplanes during takeoff. He puts into clear words a lot of frustration that many share each time they fly. While I have not historically been impacted by these rules very heavily as I prefer to read, I will be in the future as I have converted eBooks. This means no reading during takeoff - a generally boring and stressful time. Taking peoples' gadgets away forces them to pay attention to what's going on around them, increasing their ability to react in an urgent situation. On the other hand, it forces them to pay attention to what's going on around them, often stressing them out more than they otherwise could be. The music, videos, and books being denied are often coping mechanisms. Even when they're not, they're often considered one of the perks of flying rather than driving.
Here's another fun fact - one reason these gadgets are disallowed because of transmissions that they might make if they're malfunctioning. Isn't that what the FCC certification is for?