What about on my tablet, which doesn't have a space bar?
Edit: These are genuine questions, and I am deeply frustrated that it's being downvoted without any discussion. People are claiming that hitting the space bar takes you linearly through the entire presentation. How do you know you reach every slide like that?
Really, seriously, how do you know?
As far as I'm concerned the navigation is opaque - if I hit space, I don't know that I'll reach every slide.
How do you know ?!?
I suspect that people are enamoured with the attractiveness of the presentation - it's cool, it's slick, it's gorgeous, it's wonderful - and when I question its usability or discoverability, people are downvoting because they have no answer, and just get pissed off at being questioned.
Do you actually have an answer? If so, tell me.