I disagree with your post re the gender issues. But all I really want to point out is that the only time they've said the 'd' word (as you put it) is in reference to Dick Roman, as you can't say 'dick' on broadcast television except as a person's name. So no, Dean hasn't used that word like he has 'bitch'.

Won't don't/can't they have a strong female in every episode? Why not? Women make up half the population, surely it's not too much to ask or too difficult a task to feature a decent female character every episode, especially if they can do it with two+ men every episode (assuming you think the Winchesters are strong…

It's not really about them being killed off. It's how they're portrayed as characters while still alive.