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I'm in the same situation for my main keyword, I assume that it because I have always sought links using the plural form.
mens tie vs. mens ties
It just really bugs me that I have to write grammatically incorrect titles (like womens) because nobody uses apostrophes anymore!
...and another tool which for some reason got censored out when I mentioned it...
But if the widget is a $4995.00 machine, they're more likely to search for the "widget" instead of widgets (cause not many people buy more than one at a time)... They're trying to figure out intent (same as I am).
I wouldn't expect Google to return the same results for singular or plural terms (much as in some cases, I wish they would) They're trying to figure out intent (same as I am).