Link building in SEO is similar to a beautiful tapestry. Google cannot find a thread, but Google can find a well made and designed tapestry.
Having a similar thread is more pleasing to Google - no different than a tapestry with complimentary colors.
Build your articles, your websites, your comments, your photos with similar themes and you will create a pleasing tapestry that Google will reward with a higher page rank.
A higher page rank is free advertising and is a value in accounting terms called "good will".
Best of luck to all our Hubbers on that Internet tapestry.
photo courtesy of: vam.ac.uk