IE8 and lower, do not recognize HTML5 tags; it treats them as self-closing tags. In other words:
<section>Hi there</section> is treated as
<section />Hi there<section /> Because of this treatment, IE can't style them.
However, modernizr works best when using a custom build specific for your website. And Zen can't know what kind of custom build you'd need for your website.
So the next best option is to use the HTML5.js script directly. (Modernizr includes Respond.js.)
In addition, we should look at the innerShiv and the jQuery monkey patch being used in html5_tools.