[*]"Google
does seem to perceive a top level domain as
a separate word: for example, searching for [fishing net] we get more .net domains on the first page than when searching for [fishing netting]" - does this mean there is hope for .biz? Or perhaps for URL hacks like tic.kets.com?
Choose a single instance which has many unknown factors weighing on it, and infer facts based that single instance.
Faulty logic abounds. Where to start?
Get more results containing .net's with 'fishing net' than 'fishing netting'. This is true, so what does it mean?
Lets do the same thing with .com ('fishing com' 'fishing comming').
We get alot of misspellings of "coming" (who didn't see that comming!), most .coms, some .nets, and a couple others.
Looking at this as scientifically as I can, I deduce this theory:
It's possible G/Y/M search engines may interpret com, net, org, etc in the search keywords as a request from the user to provide a certain TLD.
What I find
much more likely - in all likelihood it's a matter of those sites having their domain name including the keyword (com net org) in the TITLE (Welcome to somedomain.com) and near the bottom of the site in the COPYRIGHT (copyright 2005 somedomain.com), as well as other places in the text, and also being linked to as "somedomain.ORG' or 'somedomain.COM'.
TITLE, text mentions, and inbound link text are all major and well established factors for search rankings.
Beyond that, the example fishing net is a TERRIBLE example, since "fishing net" is an expression with meaning. Google even gives "related searches". Nobody says "fishing netting". Gimme a break! When you search "fishing netting" you get a bunch of websites with "fishing net(s)" right in the title.
Even further beyond that,
when you ask a question consider the source of the answer. This is a domain forum, full of people who sell domains. It behooves them not to tell you a domain name with keywords in it is valuable in SE terms. Most of them probably believe what they're telling you (including the person who wrote the article).
It's much easier to believe something when it supports your vested interest, even if has no basis for truth.