John McIntyre tells us that Martha Brockenbrough (from the Society for the Promotion of Good Grammar) wrote to the chairman of the Toronto Maple Leafs hockey team to complain about "their irresponsible plural." I guess this is the letter, where she complains that it should be Maple Leaves.
Steven Pinker talks about this in chapter 5 of The Language Instinct - in fact he explains why Maple Leafs is pluralized the way it is.
English has two kinds of compounds: exocentric or headless compounds and headed compounds. Headless compounds are compound words where the meaning is not specified by any of the parts:
A flatfoot is not a foot, a still life is not a kind of life, a sabre tooth is not a kind of tooth (it's a prehistoric tiger), and a Maple Leaf is not a kind of leaf. Compare this with headed compounds, where the meaning of the whole compound is specified by the head word:
... which are kinds of houses, boards, and birds respectively.
Headless and headed compounds behave differently. Headless compounds are usually pluralized by adding s. It's as if the headless compound is an indivisible unit, and the plural marker can't see inside it to pluralize it according to the how the head word is normally pluralized. As Pinker says, "If low-life does not get its meaning from life, it cannot get its plural from life either." So our headless compounds above are pluralized like this:
and not like this:
On the other hand, headed compounds form their plurals the same way their head words form their plurals. So the headed compound "maple leaf" - a kind of leaf - is pluralized "maple leaves".