Well, why not throw out anything ending in .com or .net? After all, they're all made to earn revenue...
I hope the point is clear -- "to earn revenue" isn't an appropriate test. But your point is well taken. I'd prefer a search to turn up the site made by the guy in the garage who is passionate about the subject rather than the $4/hr content farm content.
I think if we're to continue complaining about spam we have to actually define what we mean by spam. And I have this strange feeling that not everyone will agree...
The about.com example shows how hard distinguishing quality algorithmically gets at the margins. You do actually find stuff on about.com now and then which is pretty decent--not great but decent. You might even say the same of ehow, albeit at a much lower rate.
On Quora, the former owner of eHow recently wrote[1] that when he handed over the keys to the people who bought the site, it had an excellent quality of content. This gave it a good 'credibility' on Google. When it was taken over, it was turned into a content farm, but the atrophy of credibility is possibly to disproportional to the spam parameter variable, which leaves it in Google's results. At least according to one of his listed explanations.
I recall about.com as a decent site a while ago, but I believe it was acquired a while ago by ... Yahoo!? Go figure.
Why does everyone keep bashing on about.com? They've been around forever, have excellent content, and I even used their resources to learn a foreign language.
They're made to earn the employers revenue, not help out people with the particular queries.