Searching for ".com" and ".co.uk"

I'm just after some opinion on this.

If you do a search for ".com" or ".co.uk" (without the quotes) the rankings
look like a list of the most important sites on the net in a rough order of
importance.

The strange thing which I've noticed is that some industries seem to be
grouped roughly together, i.e. the newspaper/news sites, job sites and a few
others.

My question is, is the ranking here determined by the amount of backlinks
where the site uses the full www.bbc.co.uk (instead of "news") or
www.amazon.com (instead of "buy really cheap books") in all their incoming
links?

Or is the grouping together a sign that Google gives a specific value to
each industry, allowing them to rank higher than a site in an alternative
industry for the same phrase? (assuming all backlinks, PR etc are the same)


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