I would imagine that David doesn't want just anyone to have his email address for security reasons, and that's reasonable. The way I see it, if David wants to start a dialogue with any of us fans, I'd let him make the first move. All we can do is ask. I've been leaving comments on his MySpace page hoping he'll see them, but so far it looks like whoever maintains his webpage doesn't pass on messages directly to David. And I doubt very much that David keeps up with his MySpace that much... he and the band are trying to get a record out, they're getting ready to tour, and Lena just moved in with him, so he's probably really busy.
Still, I'd love to be able to have some kind online friendship with David like some of us have with Ben. Just talk, pass messages back and forth, be online "pen pals" in a sense. I expect nothing more than that, and to get that would be great...not that I expect that to happen anytime soon, but it's a nice thought.