If you don't want it, you can either not broadmatch the term (just use phrase and exact, but you will lose the other broadmatches) OR (probably better) enter the misspelling as a negative word.
It has been my experience that you cannot rely on "expanded" broadmatching to find *all* the common misspellings so you should ad them as well....(if you want them)
I guess this broadmatching applies to plurals as well?
It should, but again I wouldn't rely on it. I tend to try and illuminate ALL the matches I can think of and think of Broadmatching as covering the things I have not thought of.
I keep a list of 'words to add' and once and a while go in and add them.
Broadmatching is (no longer) what it is 'cracked up' to be. Google is a little 'less than forthcoming' on its shortcomings, but it is useful.
What they DON'T tell you (clearly) is that you may THINK you are broadmatching but you might not be. They take away certain (invisible to you) broadmatches if they do not perform. The worst part is that they do this without telling you!
So if you broadmatch on widget, hoping to get red widget, blue widget, etc., at some point they may 'drop' the broadmatching (on widget) and you won't know unless you check your ads yourself.