It's not the same characters, it's from an earler generation. Those cutie marks made sense in that version. I think Sweetie Belle could still get away with a heart, but make it look more musical (I like the idea of her talents being music related), but they haven't shown anything to do with butterflies for Scootaloo yet.
why wouldn't their hair styles change with age? when you grow up you become that funky butterfly or wasp that you never expected. age is a metamorphosis, so as well as this mimics the style of the show i think it's lacking in creativity, almost entirely.