Because we all love omni-O-Rings.
But in all seriousness, this is a marvellous addition from RTR to U/W control. Putting Maelstrom Pulse on an Oblivion Ring is amazing, but that one line of text makes it so awkward...
"not named Detention Sphere"
This is obviously to prevent silly loops, but if you look at it another way it's (to me, at least) a shame it has it, since it can't be cast, targeting another Sphere, to exile both of them, so they could both come back. This would allow the first one to exile a new target as the old target came back.
Still, it's a perfect card for U/W, and it'll be a strong force that drives U/W control forwards for quite a while.