Posted on Apr 22.07 to Online Marketing |   

As far back as 97 (and probably earlier), we knew that people don’t read on the web. Jakob Nielsen recommended using bulleted lists and sub-headings back then. He didn’t use the word (as far as i know) but he was talking about chunking.
From wikipedia:

In cognitive psychology and mnemonics, chunking refers to a strategy for making more efficient use of short-term memory by recoding information… A variety of studies could be summarized by saying that short term memory had a capacity of about “seven plus-or-minus two” chunks. Miller wrote that “With binary items the span is about nine and, although it drops to about five with monosyllabic English words, the difference is far less than the hypothesis of constant information would require.

More recently, we’ve begun studying information scenting and foraging:

The “scent of information” is a working theory we use to explain how people navigate large information spaces. Users scour pages for strong scent, using those clues to help them know where to click.

User’s click (and enjoy) on links that give off the scent of a useful page.
I would assert that headline structures like top 10s are successful because they give off the scent of chunked (and therefore useable) content. Even headlines that announce some sort of instruction imply that the content is chunked into instructional steps.
Of course this is more of a usability, a friction-reduction point than a persuasive one. The user must still want to click (or vote for) the headline.

This also suggests that 5 or 7 is a better amount of chunks for written content than the more common 10.