This is old news, so my hope that it means something has died. But I actually hear that there are copyright issues being worked out with the rerelease. Like in StarTropics, the Island Yo-Yo is renamed the Island Star because Yo-Yo is copyrighted in Canada. There are a bunch of yo-yos in EarthBound, of course... calling them all, "Star," "Trick Star," "Combat Star," would be pretty confusing as to what you're "shooting." I mean, what do you call a yo-yo if not that?
But... I never use yo-yos or slingshots in EarthBound. Their superiority over other available weapons is usually not very significant and otherwise short-lived, and you can't score a "SMAAAASH" with a shooting weapon. So I wouldn't really care if they just got taken out of the game.