W3C Validation of WP Theme

Hi everybody.

I’m trying a lot of WP themes but most of them don’t pass the W3C validation.

For example, the default theme twenty elevent has the following errors:

Line 73, Column 209: Attribute pubdate not allowed on element time at this point.
…me="2012-07-25T15:15:04+00:00" pubdate>luglio 25, 2012</time></a><span class="…
Attributes for element time:
Global attributes
datetime
 Line 85, Column 223: Bad value category tag for attribute rel on element a: Keyword category is not registered.
…i gli articoli in Uncategorized" rel="category tag">Uncategorized</a>			</span>
Syntax of link type valid for <a> and <area>:
A whitespace-separated list of link types listed as allowed on <a> and <area> in the HTML specification or listed as an allowed on <a> and <area> on the Microformats wiki without duplicate keywords in the list. You can register link types on the Microformats wiki yourself.
 Line 124, Column 109: Bad value generator for attribute rel on element a: Keyword generator is not registered.
…aforma semantica di editoria personale " rel="generator">Utilizza WordPress</a>
Syntax of link type valid for <a> and <area>:
A whitespace-separated list of link types listed as allowed on <a> and <area> in the HTML specification or listed as an allowed on <a> and <area> on the Microformats wiki without duplicate keywords in the list. You can register link types on the Microformats wiki yourself.

How can I fix theme problems of twenty eleven or where Can I find really W3C-valid themes?

Thanks!