I think we are mixing two different things here.
There is huge diference between Stephen Hawkins' books and London's Yellow Pages. They are of different kinds. While a normal site can be equated with books, a web directory is more of an online Yellow Page listings where people find websites that are arranged categorically and based on rankings, Other websites are more like Books that need contents.
Hence, a Directory's content is totally different from a normal website's content like bbc.co.uk. A directory's content should be how many sites are listed there and what are the qualities! The more number of quality site a directory posses the richer it is iin contents.
Whereas BBC site's content should be related to news or related items.
As
John so thoughtfully pointed out-- mere quality contents will not gurantee high ranking on SERPs --but quality contents with quality backlinks will surely quarantee that.