Yeah, my point wasn't so much that there are not exceptions, but that there are frequent patterns in the English language.
Rather than throwing up your hands in defeat and saying, "The English language is totally inconsistent; the only way to learn it is to memorize each arbitrary word form," the key is to familiarize yourself with these patterns so that at a minimum you can make a better guess next time.
Hopefully, WA learned today not just that the plural of "life" is "lives" but that, in general, when a noun ends in -f or -fe it usually changes to -ve. So if tomorrow he sees a sign that says "5 loaves of bread for $1" it won't catch him off guard like the title of this submission did.
The last example is a proper noun(-phrase) and wouldn't necessarily follow the "standard" pluralization rules anyway. If you think about it you're not making "Leaf" plural you're making the noun-phrase "Maple Leaf" plural, and who knows what rules apply then.
life -> lives
wife -> wives
elf -> elves
half -> halves
leaf -> leaves