Comment by wxl

I was about to say it may have something to do with the fact that they're separate letters in other languages, like in Polish ą is a different letter, as are ć and ź. It may have something to do, though, with the fact that the ą sounds very similar to a, but ć and ź sound much different from c and z. (I'm only speaking from my very limited knowledge of Polish, I'm not sure about other languages.)