Every new Apple mobile device and every new Mac — along with the latest version of Apple’s Safari web browser — supports web standards including HTML5, CSS3, and JavaScript. These web standards are open, reliable, highly secure, and efficient. They allow web designers and developers to create advanced graphics, typography, animations, and transitions. Standards aren’t add-ons to the web. They are the web. And you can start using them today.

via Apple – HTML5.

The site also has examples showing you the difference between HTML 5 and Flash