Hmm. It's been a few years since I saw you speak in person, but at the very first startup school (2005?) I thought your presentation was perfectly fine.

In other recorded presentations of other events it just seems like you take the casual/personable approach to a presentation vs. an overly formalized approach.

I would not give you any negative points for your stage presence at these events. I would suggest some more upscale footwear at times though...