Re: notifying particular thread to wake up.

There's a big difference -- we're discussing information and text here
rather than physical goods that are actually scarce. People would not
expect to find a salad for free; or for that matter to find anything
for free after "going to" a store. On the other hand, if someone says
"the information you need is at this URL", the normal thing to find at
the indicated URL is ... the information in question. Not some ad
trying to sell you something, but the information itself, since it
could easily and cheaply be there, and 9 times out of 10 it actually
is. Links to Sun's Java pages and Roedy's site abound in this NG.
Following them leads directly to what someone said would be there.
Then along comes a link like yours and instead of the information
itself is a page saying "We have this information but we won't let you
see it until you pay up". How nice. And no warning of this difference
was in the post with the URL, either.

Same goes for software as for information. People posts links for the
JDK itself, for Eclipse and NetBeans, etc., and readers can follow
those links and download and install away. Then comes that odd link
that instead leads to an ad or a paywall of some sort instead of a
free download.

Links to non-free software or information should be clearly marked as
such in the newsgroup postings, and good free alternatives should be
mentioned as well so that people may make an informed choice, and so
that people that aren't Americans with credit cards and decent amounts
of wealth can actually get some use at all out of your post.

That is not, in and of itself, a problem; it's the sneaky lack of
disclosure that is. When URLs are posted to things that might well be
directly readable or downloadable for free, you should at minimum make
it clear in the case that the thing is not that available.
International and relatively poor people (and this group gets a lot of
students, and students are frequently a) foreign and/or b) poor) can
immediately see that the link will be useless to them. People in
general will know what to expect. Of course, if there's known free
alternatives it would be good to mention these too. Conspicuously
omitting to mention these may do harm by leaving people to make a less
informed choice and denying any useful options entirely to some
people, and may also cast doubt on your motives. And of course if (as
is the case with amazon.com book-purchase links, last I heard) you get
a kickback for referrals disclosure of that, too, is definitely
warranted.