Does Domain Extension Matter?

Some countries have certain rules which make it harder or more expensive to get a local domain than a global one. For local search queries sites which match the local domain extension or are hosted on a machine in that country may get a boost in relevancy over global domains. (ie: .uk may rank well in UK, .de may rank well in Germany)

Google can use the increased price of local hosting and/or the rules associated with gaining a local domain extension to assume that locally hosted or locally registered domains may have a greater local relevancy.

Likely due to less spamming incentive, a smaller content base, and a lesser understanding of local language many of the filters that are applied to the global search results may not be applied to some local results.

By looking at link reputation scores Google lets pages on websites vote for other pages. On the commercial web the purity of many votes may be in question. Weblogs Inc., for example, has gambling ads on over 40 of their blogs - in spite of Google being a minority owner in that network.

In a recent WMW thread someone mentioned this URL (maricopa.gov) as a .gov domain that accepts advertising links, but generally it is much harder to buy .gov or .edu links than .com or .net links.

Beyond .edu and .gov there are also other rare domains which people probably do not talk about that much which also have similar importance. In the UK .ac.uk is the equivalent of a .edu, and perhaps some .mil extensions may be trusted a bit more than the average .com, .net, .info, or .biz type domain.

The factor of trust would be three fold:

• The standards required to get a .edu (or other rare domain extension) implies a certain level of credibility.

• When the web started educational institutions and governmental bodies were at the core of it. Thus, with greater history, they are more likely to have more link equity. Over time webmasters of scraper sites and legitimate web pages are going to be more inclined to link at the top ranking pages, which reinforces the link popularity.
• Generally much of the well cited college papers or governmental pages are of higher quality than the average web page due to internal requirements. On top of that they are harder to influence than most average web pages. For example, it is pretty damn hard to get a professor to link at your site or update his or her outdated links. No professor wants some random self promotional asshole (which is how they will view many people who contact them) telling them that their content is outdated or inaccurate.

When you read about Trustrank the seed set of sites were all backed by government, educational, or corporate bodies. If you don't think Google relies on third parties in this way think about how they limit what sources they accept for their local search product or for their news search.

Surely many college students are selling .edu links by now, but those are still a bit harder for the AVERAGE webmaster to find than .com links for sale.

That which is rare, hard to obtain, hard to influence, or vetted by other trusted bodies may aid in relevancy scoring.
It has been a long time since a link is a link.