That would be a good theory if their page wasn't titled "HTML5 and web standards." There's not much room for interpretation in that.
I suspect that they simply let their desire to make the demos really impressive distract them from the original point of the demos. They could, I imagine them thinking, make some cool demos that would work in Chrome and Firefox and Safari, or they could make some even cooler demos that showed off things only available in Safari, and have a nice way to promote Safari to boot.
The problem is, once they did that, it went from a showcase of HTML5 standards to a showcase of proprietary Safari features that might be standards eventually. Oops. I'm rarely critical of Apple, but this is one of those times that makes me wonder if anyone there had their brains turned on.