First, I would hope that to “question age-old search engine optimization wisdom” is not disparaging to you or your readers. Anyone who does not continue to test these is destined to fall behind the curve.

Second, it would be horribly ludicrous for Google’s algorithm to be susceptible to simple on-page keyword placement. Google began devaluing these tactics with the keywords meta-tag years and years ago, and it makes sense they would continue to do the same.

Third, if on-page optimization was of high importance, it would be nearly impossible for Google to discern between the myriad competitors which could implement near identical keyword placements and HTML optimization throughout their page. Google has to figure out a way to rank pages 1 to 10, even if all pages score a perfect 100 on the on-page relevancy tests. Thus, the optimization techniques which make the marginal differences are off-page.

Finally, I made it clear in my post that these were preliminary results and that the results do not take into consideration any synergistic relationship between multiple keyword placements. Instead, they merely describe that there is virtually no difference in the ranking power of keywords that occur within various tags on a page. A single keyword in plain text on your page is every bit as valuable as a single keyword in an H1 tag. The results were confirmed at a macro level by SEOMoz’s study which looks through a real dataset of billions of pages.