No matter what the subject, if you approach it with enthusiasm, your audience is likely to be interested too. Energy spreads, and the lack of it can kill a presentation. I find that a responsive audience feeds my energy and can make me better as the presentation progresses.
That's part of the trouble with webinars. You don't have access to as much audience feedback. You are staring into a blank screen when you present online. It's up to us as presenters to find a way to keep the energy going - whether you are in front of a live audience or presenting to a muted crowd on the web.
Humor is one of the things I use to keep my energy going - I entertain myself. So even if I can't tell if anyone is listening or responding, I still get more energy by adding humor.