Everyone knows that Mario is a prime example for the neverending struggle between an oppressing force and opressed forces fighting for their right. Disguised as a game about a plumber saving his Princes from the claws of a fire-breathing dinosaur turtle (clearly a metaphor for outdated or unrealistic forms of governments).
Excuse me while I fetch the Brain Bleach (tm).
But seriously, beyond the Storybook, introduction, and star-creation theology (each of which the player is not required to follow along), there wasn't anything too complicated in SMG1. Granted, now that SMG1 had all that much story in it, I think it would be a good idea to let the story cool its heels a bit and get back to the gameplay, then, make 3 a closure with a good balance of story and gameplay depth at just above moderate.
So when Miyamoto says there won't be "a need" for that story depth, he's right. We know who Rosalina and the Lumas are, we know how the heck Bowser got his power (and, being the bad magician he is, performs the same Grand Star trick again
), and we've got more explanation as to how the bright and cheery magic of the Mario universe works. Great, good, done, now, let's get back to the fun. And between the saws and Yoshi, I'm having a lot of SMW flashbacks, and that's a good thing (eat your heart out, Martha).
NOW WHERE THE HELL IS MY ROSALINA, NINTENDO?! CHOP CHOP!