These are ‘tit-for-tat’ links. For instance, you make a deal with your friend who has a business website to have him place a link to your website, and in exchange your website links back to his. In the dark ages of SEO, this used to be somewhat effective. But these days, Google considers such 'link exchanges' to be link schemes, and you may get hit with a penalty if you're excessive and obvious about it. This isn't to say that swapping links is always bad, but if your only motive is SEO, then odds are that you shouldn't do it.
On the other hand, all of the results for the PageRank engine (aside from a single secondary listing) link to the homepage of major American universities. The results are much more logical and useful in nature. If you search for “university,” are you going to want the homepages for popular universities, or random subpages from a sprinkling of colleges all over the world?

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