Toshiba, Sony and Zen paid Amazon cash to have those products highlighted on the 'advice' page - it's got nothing to do with their opinion. Many retailers do this both online and in catalogues to offset the costs of copywriting / photography etc.
Most people won't click on the buying guide anyhow. They'll just go to the MP3 player home page where iPods have 5 of the 7 image slots above the 'fold', 4 of the top 5 best sellers and a selling page of their own.
I think he's getting at the basic shape/layout/design.
All/most consumer guides involve paying to get in/higher ranking.
AAA for example wasn't listing certain restaurants in Chicago even though these restaurants had been, and still were extremely popular and nice places in general.