As of the March update, Google is now using the comment dates to date articles:

Improvements in date detection for blog/forum pages. [launch codename "fibyen", project codename "Dates"] This change improves the algorithm that determines dates for blog and forum pages.
Unfortunately, they are using the oldest comment date, so even currently active posts appear to be out of date.

This is an annoyance for those of us who have already removed all date features from our posts and pages by editing our themes.

Unfortunately, you cannot remove dates from your Wordpress comments by editing your theme -- you have to hack into Wordpress itself.

The file to edit is wp-includes/comment-template.php. Edit line 1365 to replace this:
printf( __('%1$s at %2$s'), get_comment_date(),  get_comment_time())  ?></a><?php  edit_comment_link(__('(Edit)'),'&nbsp;&nbsp;','' );
With this:
printf( __('%1$s at %2$s')) ?></a><?php edit_comment_link(__('(Edit)'),'&nbsp;&nbsp;','' );
Remember that you will have to replace this hack after every Wordpress update.