My take on this is that a character wouldn't be able to wish for a feat because to a character a feat doesn't exist. It's like Attack Bonus's and AC...the characters have no idea what these things are it's like one PC asks another PC what level he is. In game it doesn't exsist. Character's don't know what feats are, the player gives them the feat that goes along with the characters fighting style, kinda like he bettered a new technique or became better with his weapon. For a character to even be able to wish for a feat he would have to word it right. In example, a character that wanted to gain the Quick Draw feat would have to say: "I wish to be able to draw my weapon faster." or for something like Weapon Focus: "I wish to be better skilled with my weapon."
In conclusion a character can't directly wish for a feat but can wish to be better skilled at something!