To a point, but the game world is created using the real world as a model. Mathematically (by the RAW) this can be done, but is it plausible, even in a fantasy setting (kind of like 'I can effect my own frame of reference, but can I move faster than light')
Explain why it isn't plausible.
Now it has been stated that an ally can be used, if said ally was previously (or still) an enemy. How does the 'Summoned Creature' tactic fit this senario, given that said creature is not a construct. Heck, what if it is a construct? How would you be able to take an AoO on something doing what your allie has told it to do? If you can hit your ally, why create the set up to begin with?
Any character that is next to another character that performs an action that normally provokes an AoO should be able to take that AoO if they choose. What is magical force is protecting a fellow PC when he drinks that potion in the square behind my character when my character threatens every square around him - other than using metagame knowledge that in one section of the PHB when describing AoOs the word enemy is used?
As to the why summon a creature/create an astral construct - it is very simple. In some peoples games there is no morality question about how these creatures are used.
It seems (to me, milage may vary) that this is metagaming, as it cannot be explained in any other way than 'the rules allow (or do not disallow) it to happen'.
Right back at you. Explain why, other than AoOs can only be taken against an enemy, why it can't happen. You are also metagaming.
As for your real time example. The game world is different than the real world. In a game world where there is no moral problem with how summoned creatures end their existance on the summoners plane - it is simply an AoO/cleave - like every example you have provided.
There are so many things in the game that you wouldn't do in the real world that it isn't funny. Here is a simple one. Unless you were in truly dire straights you wouldn't jump off a hundred foot cliff and if you did, you wouldn't expect to be more or less fine. In the D&D game I have seen high level characters do that without a second thought - why because they know that in their world it is almost imnpossible for such a fall to kill them and if it doesn't kill them, it won't even slow them down. Meta gaming? No, heroics - just like in umpteen thousand stories and movies.
The game world is different. Your real world model falls flat in so many places that it isn't helpful. So repeating "you wouldn't do that in the real world" is completely unhelpful.
I can't explain it any better.
I can't even fathom how you can't understand how this could happen in someone else's game with a different morality about summoned creatures.
Ciao