Planet13 - 6:59 pm on Jun 5, 2012 (gmt 0)
This isn't an example of a penalty at all. It simply shows that the page is better optimized and ranks better for the singular term than the plural.
I appreciate your input, but I respectfully have to disagree (read below for explanation why). You may be right, but I suspect that you are incorrect in this case.
Isn't it possible that the Google algorithm has judged the page to be OVER-optimized for the plural form, in which case this would be the result of a penalty?
I believe in my case it was because, prior to Penguin, my blue-widgets.html page was ranking #9 for the keyword "blue widgets"
After Penguin, it wasn't ranking there anymore. Instead the HOME PAGE was ranking in it's place for #9. the blue-widgets.html wasn't ranking for "blue widgets" in the top 100 results (stopped searching after 100).
and as I mentioned, the singular form ranks where it used to (around #13)
Important note: the home page links to the blue-widgets.html page using the keyword "blue widgets" as the anchor text, and the home page DOES have the words "blue widgets" in the title (as does the blue-widgets.html page), and the domain name does have the word "blue" in the URL.
also note that the blue-widgets.html had a LOT of text on it, despite being an ecommerce page. So there were many instances of the phrase "blue widgets" on it.
the only page in the top ten SERPS with MORE text on it than my page was a wikipedia page (which, of course, cited my page as a reference).