Earlier this year, the w3c validator switched to a new engine and although this returns results for html5, the service was no longer returning simple statistics in the http header. In short it broke Scrutiny's html validation feature. (Those using a local instance of the validator may have found that it kept working)
My options were to screen-scrape from the new w3c validator, find an alternative service (either web or something that could be included within Scrutiny) or to write my own.
In the absence of a 'quick fix', I replaced the full website validation feature with a 'single page validation' (context menu item in SEO table).
Feedback has been generally good, some users agreeing with my own feeling that because websites tend to be based on template(s), validating all pages isn't necessary. For this reason, it's unlikely that the new tool mentioned below will be part of Scrutiny, but I may include it in the dmg as a separate free app.
I have now found an alternative, that works well and doesn't rely on a web service or need anything extra installed. It does give slightly different results to the w3c validator, but I guess any two tools will give different results.
My first prototype is now working, if you are interested in being able to scan your site, validating the html for all pages, and would like to give this tool a whirl, please just ask.