The idea that the focus of a site is important has merit. However, that doesn't explain the retail store's site that I created. Its focus is on the store. Its focus isn't on Acme widgets, or Brand A widgets or Brand B widgets. But it's ranked page one for those phrases and others for several years.
If site focus is a major factor, this site should have been Pandalized quickly.
If I do a search for Brand B widgets, Google's first page has the first three links being to pages on the manufacturer's site, the next being a link to the Brand B page of a large widget classifieds site, then a link to the retail store's site, then a link to a widget ecommerce site, then a link to a forum about widgets, then a link to a page on a widget parts site for a certain part for Brand B widgets, and finally a link to a forum thread about Brand B widgets.
The two forums and the widget parts site aren't very focused, and neither is the retail store's site.
My site has Brand B widget pages, and then a drop-down menu to find retail stores that advertise on my site that mention Brand B as one of the brands they carry. That seems as focused or more focused than the forums or the parts site.