Comment on WordPress Gravatars by SEO Dave.
You are right, have tested all the Gravatar settings and those two with Stallion aren’t working as they should. Have to admit I’ve never used those two settings on a site, had to check what it was meant to look like in TwentyTen :-)
It’s probably the custom code I’m using to pull the Gravatars, I’m showing the Gravatars as a background image (using CSS) rather than an image loaded as part of the page for SEO reasons (no wasted alt text which could have an SEO impact).
Will take a look if I can find a fix, but from an SEO perspective removing the images so they aren’t considered part of the content is more important.
Update: fixed in the next theme update