Why the Toronto Maple Leafs are not the Toronto Maple Leaves

If you've lain awake at night pondering this question, the answer is now available, courtesy of bradshaw of the future:

English has two kinds of compounds: ...headless compounds and headed compounds. Headless compounds are compound words where the meaning is not specified by any of the parts [such as "still life" or "Maple Leaf." A still life is not a kind of life (it's a kind of art work), and a Maple Leaf is not a kind of leaf (it's a hockey player).]

Compare this with headed compounds, where the meaning of the whole compound is specified by the head word: doghouse, blackboard, blackbird... which are kinds of houses, boards, and birds respectively...

Headless compounds are usually pluralized by adding s... 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... still lifes [and] Maple Leafs...

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". 

More at the link, which I've excerpted here.