Thx for your reply. I apologise if all this seems pedantic, and I should clarify that I am only concerned because I am trying to troubleshoot a Google penalty for another site. I usually don't see an issue with such small things, but in this instance, with my desire to get to the bottom of Google's behavior, I have vowed that no stone shall remain unturned.
You are correct about the validation, I must have accidentally checked as XHTML 1.0 Transitional. I went straight from Web Developer tool bar in FF...
However, Google is quite clear about hidden text and links, and the below would appear to potentially still be in violation (who knows with Google...):
<a rel="nofollow" id="cancel-comment-reply-link" href="/pianolesson-nine-the-diminished-chord/#respond" style="display:none;">Cancel reply</a>
Here is a page with comments from a site based on the popular Motion theme:
This has the exact same markup generated as in my Mother's site. However, the theme developer has built it as XHTML 1.0 Transitional, so in this instance the same output does not validate:
It seems to me that Akismet is generating invalid HTML if it is used on an XHTML 1.0 Transitional theme?