HTML5 has something called canvas that can show beautiful charts like this.
Now, do draw a chart, we need data primarily. That is xml, json or javascript array or something like that. HTML5 is just the latest version of HTML which makes it a Markup Language.
HTML just can render graphs into the screen once your script supply it all your data.
The point is, HTML5 cannot parse your custom data. And also to make it compatible to our good old IE, who apparently have not heard of canvas yet, , we need libraries like explorercanvas.
And to make this drawing simpler and cross browser friendly, we use libraries like