Relevance: SERPs and Related Searches

Google R&D discusses an enhancement to its related search links in an article: Fresher related search suggestions.

Let’s try to search for the animal: cat.

If you enter into Google search the keyword cat, the following links to relevant SERPs display down the page:

• Caterpillar Inc.
• Cat - Wikipedia, the free encyclopedia
• Centre for Alternative Technology Home Page
• Lolcats ‘n’ Funny Pictures of Cats

The following related search links are displayed at the top of the page:

• cat deeley
• cat stevens
• cat unix
• cat exam

Why is there such a divergence between the concept of “relevance” for SERP links and for related searches links?

If Cat Deeley, a DJ, is relevant to related searches, why doesn’t she appear as a SERP link?
If the Unix command cat is relevant to related searches, why isn’t it listed as a SERP link?
Similarly, if Caterpillar Inc. is a relevant SERP link, why isn't there a related search link to building equipment?

In my opinion, applying two widely divergent standards for “relevance” to SERPs and to related search links introduces the risk of reducing the coherence of the Google page rank algorithm.

Relevance to a keyword/s such as cat means one thing across the top of a page, and something else down the page.

btw check out my original SETI research