dirty and filthy

dirt poor vs. filthy rich

have you ever noticed how the two expressions which describe being at either end of the income spectre both involve being the opposite of clean?
i wonder why that is? could it be that both deem money to be dirty? well that doesn't work, cause 'dirt poor' still implies that you're uncleansed...even without money!! poor as dirt! is that what that means? is dirt poor? how do you know that?
but if someone's rich, their automatically deemed to be filthy??? so money makes you dirty...but being poor is also dirty?
so the middle class are the only clean ones??? that hardly seems fair. where's the happy-medium??? can't you be just a little dirty?? or halfway clean? or can you be both dirty and filthy?
interesting concept, huh?

discuss.