Yes it would.
From [adwords.google.com...]
Broad Match - ... <snip> ... Your ads will also automatically show for expanded matches, including plurals and relevant variations.
arran.
It works fine, but if the plural is an important one I would suggest writing an ad that uses the plural. Broad match will not highlight widget in your ad text if it matches against widgets.
I may also help the quality score (but then again, so might crossing your fingers).