I think Stack Exchange and Wikipedia are examples of SEO'd sites too. For example: Stack Exchange had problems with indexing before they added a sitemap [1]. Wikipedia takes a lot of care to create machine-indexable pages with quality content, that link back to their sources [2] and are linked to internally. Both follow SEO best practices as described in the Google Quality Guidelines [3]
Or your definition of "SEO'd" is leaning more to manipulative/sleazy.
In your example about the spectacle cases, would the other site being an affiliate make a (huge) difference? If Google punishes companies that have more than one website, people would shift to affiliates or try to hide they own the websites in other ways. In a way I feel multiple McDonalds in one city is perfectly possible. However, there needs to be a balance between the "best" websites (be they from the same owner or not) and diversity of the results (a query deserves diversity).
[2] http://www.mattcutts.com/blog/pagerank-sculpting/
"In the same way that Google trusts sites less when they link to spammy sites or bad neighborhoods, parts of our system encourage links to good sites."
Or your definition of "SEO'd" is leaning more to manipulative/sleazy.
In your example about the spectacle cases, would the other site being an affiliate make a (huge) difference? If Google punishes companies that have more than one website, people would shift to affiliates or try to hide they own the websites in other ways. In a way I feel multiple McDonalds in one city is perfectly possible. However, there needs to be a balance between the "best" websites (be they from the same owner or not) and diversity of the results (a query deserves diversity).
[1] http://www.codinghorror.com/blog/2008/10/the-importance-of-s... "We knew from the outset that Google would be a big part of our traffic, and I wanted us to rank highly in Google"
[2] http://www.mattcutts.com/blog/pagerank-sculpting/ "In the same way that Google trusts sites less when they link to spammy sites or bad neighborhoods, parts of our system encourage links to good sites."
[3] http://support.google.com/webmasters/bin/answer.py?hl=en&ans...