Hi Eric,
I think you are on to something here. We will have to think on how to make Limesurvey usable on Tablets and Smartphones.
At the moment, there is little you can do, because radio buttons and check boxes are the browser standard buttons.
However, I was looking into the option of customizing the standard buttons and substitute them by images. There is one example in the work around section and then there is a thread of me, with another plugin for Jquery. I couldn't get it work, but tpartner seems to have found a solution. But I couldn't follow up on it so far, because a lot of other projects came in between. But maybe you can have a look at it. I will see if I can find the thread again.