The “planets” example admit the MWI is correct. Without MWI, the quantum trigger is exactly a normal random trigger, not killing 9/10th of the worlds, but killing everyone with a 1/10th probability. The thought experiment is a way to force people to quantify their acceptance of MWI.
Communication. There is no communication possible between the MW, while there is between the planets, and that will have massive long term effects.
There are two differences I can see :
The “planets” example admit the MWI is correct. Without MWI, the quantum trigger is exactly a normal random trigger, not killing 9/10th of the worlds, but killing everyone with a 1/10th probability. The thought experiment is a way to force people to quantify their acceptance of MWI.
Communication. There is no communication possible between the MW, while there is between the planets, and that will have massive long term effects.