The most important thing for SEO has always been content that people want.
For most SE's, anchor links need to be from a page with content related to the content of the page they link to - those pages that link to the Bush bio also reference him several times - not just link to him with specific text. The linking page also usually has to have a higher page rank than the page linked to to be counted by the SE.
The only thing certain about SE's is that their criteria constantly is tweaked to deliver pages relevant to the people who use the search engine. What was good SEO in January, may not be good in July.