From Joost's post on his blog: "I've since emailed the theme authors and they're taking action to fix it, so there's no reason for me to name them here, ..."

Really? By linking to the blog in question you actually very clearly named them. "View source" is not exactly rocket science and the type of people that read your blog know exactly how to do that.

Thanks for making other authors aware though of this sort of issue though. I generally tend to leave SEO to plugins and code my themes with the proper heading tags and do as much as possible to make the code lightweight. So far it's worked out fine.