No one knows how exactly search engines work. But, based on known facts we can make some reasonable assumptions.
Fact 1. The most important goal of good SE is to provide user with correct information regarding site content.
Fact 2. The content that user sees may differ greatly from the html code.
Fact 3. Now it is almost 100% known that search engines ignore 'description' meta tag. The reason is that it's content is not what user sees. Using this tag was an easy way to fool SE and make it fail it's main goal (Fact 1.).
Fact 4. The <h1> element is not user visible. It is easy to make text within it look like a paragraph text or even be completely invisible. If SE would rely on it, it would provide another way to fool the SE just the way description metatag did.
Fact 5. The Google guide does not guarantee that anything recommended will be used by SE. Read carefully, they don't make such claims. These are just general recommendations similar to W3C. Not a single word about how SE will interpret these tags.
Bookmarks