Originally Posted by
Steve in Olympia
"Use apostrophes to form plurals of letters, numbers, abbreviations,
and words referred to as words.
Examples: Please distinguish between your i's and your t's.
Nathan's 7's often look like 9's
The VIP's arrived at the gala opening of the new
play.
You used too many and's in your last paper."
http://rwc.hunter.cuny.edu/reading-w.../apostrop.html
Clearly a large part of the US population is descended from greengrocers who fled from England in the 17th century.