Third, I don't see any reason to want to come out to my parents, although this may have to do with the nuances of their attitude. I think my parents (or at least my dad) wouldn't mind me being gay, as long as I didn't tell them about it. And if so, why should I disrupt their tranquility?
For some people, this may make sense. If the parents will never come to terms with it at all, and are likely lying to themselves about what is going on because they recognize on some level they can't deal with it, then there is nothing else to be done.
On the other hand, by continuing to keep your life separate for them as you get older and assert your independence, you are denying both of you the opportunity for a full and honest relationship. You open the door to perceptions of hostility, ungratefulness, and lack of respect. You may be presuming bad intentions, obliviousness, or an unwillingness to adapt that is not present. My father was not happy, and is not happy, that I am gay, but our relationship was worse when I was keeping it a secret from him and he felt angered and disrespected that I kept him at arms' length and resented him for reasons he could not control. Now, everything is better, even if it will never be perfect--he loves my partner and I've managed to make us full members of the family, even if I know he will never be completely comfortable.