Firstly, I do disagree with your analysis about James and John because I don't think James was there for Jesus to ask. John is the only disciple who is Biblically supported to have actually witnessed the crucifixion. However, with regard to your above, intellectually, I have to concede that you make a valid point. I honestly don't know how or when the idea of Mary's perpetual virginity became a part of infallible Church tradition.
There is of course also the question of why, from the earliest times of post New Testament Christian literature, she is referred to as "the Virgin Mary." If she had gone on to have sexual relations and bearing multiple other children, I find it hard to see why she would have received that title in the Church. ...
Now here you lose me. :) The whole point of (what I would call) "The Immaculate Conception" was that Mary was a virgin when she gave birth. That made it divine in nature, and different from anything else ... ever. Her virginity defined the holiness of the event. That is certainly worthy of Church recognition, absolutely independently of whether she continued a normal relationship with her husband after the birth of Christ.
The Immaculate Conception is the dogmatic teaching in the Roman Catholic Church that Mary was born without original sin and remained sinless throughout her life. It doesn't consider her virginity.
Regards
The Immaculate Conception does not refer to the virgin birth of Christ, but rather is a uniquely Roman Catholic teaching. It teaches that the grace of Christ's sacrifice on the cross was "preveniently" given to Mary at the time of *her* conception in the womb of Anna.
It thus teaches that Mary was born without original sin of any kind and furthermore was specially filled with the Holy Spirit from the time of her conception -- filled with so much grace that she had and has "extra" grace that she can dispense to the rest of us if we pray to her and ask for it, etc.
The Orthodox Church does not accept this teaching. We believe that Mary was conceived in the same way that any other person was. We believe that the "original sin" that man is born with is the tendency to corruption, sin, and death. We believe that Mary was born with all of those things just as we are. We do not believe that a man is born with original guilt such that his default setting is to go to hell, but rather believe that we sin because we choose to, giving in to the innate corruption and weakness within us. It is our sins that we actively commit that turn our faces towards hell and the devil. We need the grace of Christ to be forgiven for all of our sins.
What we do believe is that from the earliest moments of cognition in her life, Mary chose to turn her face toward God. The Church teaches that she was born into a highly devout immediate and extended family, and that she was reared in purity. Someone once said that the whole history of the world, the whole history of that golden thread that runs through the Old Testament, is to tell us the story of how all of history came to a point with this family, this couple, this girl. The girl who would change the world because of her purity and obedience to God.
In other words, the Orthodox Church believes that Mary had no spiritual tools at her disposal other than the ones we have. This is what makes her sinlessness so remarkable, and what made her a worthy vessel for bringing Christ into the world. It is also what makes her an example for us that we can follow. If she was a "superwoman" filled with so much grace that it was impossible for her to sin, we can hardly use her as a model for our own lives, can we?
The fact that she was subject to the effects of original sin is borne out by the fact that she grew old and died just like everyone else. I would note that there are some Catholics who believe that she did not die, but was assumed into heaven without having died. This is a logical outgrowth from the idea of the Immaculate Conception -- if she was not subject to original sin... how could she die?