I think it's more a way of saying the word ... dirty implies unwashed etc ... but durty (to my mind anyway) means something slightly more "Adult"
Dirty Durty
I would have said example 2 was more like filthy
Or is that Feelthy
I dare not click, I dare not click, I dare not click, (but I really want to), I dare not click, I dare not click, I dare not click, ...
Oh no, it isn't