Phillip, this is an idea for you to develop further.

Who "mentions" the other more google or Yahoo.

I tried to do this search:
google.com/search?hl=en&q= ...

and this:
google.com/search?hl=en&q= ...

got the idea?

These numbers are relative :
Google in Yahoo! sites : 2,030,000 / 99,500,000
Yahoo in Google sites : 671,000 / 7,370,000