If you saw the debate, you saw the moderator trying to get them to engage each other. It was an unusual format and I think neither were used to that format. I thought Obama was trying to engage McCain after moderator prodding, but McCain, not so much.
Also, using his frail body as an excuse for not being able to turn and talk to someone, or type on a keyboard is getting a bit ludicrous. He is able to write and take notes and use a cell phone on camera and he did father a couple children, so I don't think that agrument hold up real well. Foxnews makes the same excuses for him.