Why rivals Google and Apple agree on HTML5

They don't agree, they both need it to be ahead of the competition in the web arena. Microsoft lost a lot of time trying to hold the web back while they milked the most of the desktop world. Now they are catching up in desperation as they see their internet flagship IE sink to lowest levels ever.<p>So, all agree in HTML5, they all support it, because they all need it.

Google and Apple benefit from the volume of sales of apps through their "app" stores. By supporting a standard (and helping it be a good one, not one that has many proprietary interpretations), they can help extend the reach of apps, reduce development cost/time of app developers, and possibly increasing the volume of apps that get sold through their stores.

This article says a lot about HTML5 but I don't think the author actually knows what it is. He's not a programmer and he seems to start from the position that programming languages are things which can be "owned."

I think he's trying to say that Apple don't view it as a zero sum game in that they either get ios developers or some other platform does. By promoting HTML5 everyone gets those developers, including them, and so if everyone developers in html5 they essentially have all the competition plus who ever is natively developing, so they have access to a host of programs that might otherwise only be available on competing platforms.