Unless I'm missing something, I don't think that Guitar Hero or Rock Band would fall under the category of "blockbuster" game. In fact, I think they are a great example of what sells well on Wii. They are simple concept games that are easy to understand and pick up and play without much instruction. The main reason for this is the guitar controller. Everyone knows how to play a guitar, even if they lack the musical talent and/or finger dexterity to actually do so. A guitar is something that everyone is familiar with, and playing Guitar Hero is already something that everyone knows how to do.
Nintendo found similar success with Mario Kart Wii and the packaged Wii Wheel accessory. It seems a lot of long-time game players hated the wheel and called it inaccurate, but it wasn't designed for them. It is for people who find the traditional controller intimidating. A steering wheel is something that pretty much everyone is familiar with and knows how to use, so no instruction is necessary. Everyone already gets it. This, I believe, is the majority of the type of audience who purchased Guitar Hero and Rock Band on Wii.
Is Metroid Prime 3 a "blockbuster" game? It is "huge, expansive, and immersive," which was how Lindy described games on the PS360. It sold 1.5 million copies (right?). The Metroid Prime Trilogy contained three of this type of game and sold even worse. Compare that to the best-sellers on Wii, and the best-sellers on other systems, and that number doesn't match up. It is a high-quality, well-reviewed, marketed, and Nintendo-published title, so none of the grab bag of excuses for low sales can really apply. This is a game which should have sold to everyone who had an interest in a "blockbuster" type game, and, well, I believe that it did.
There are a few other examples I can think of which might qualify. Batallion Wars II from Nintendo as well, and the aforementioned-by-Broodwars Fire Emblem. No More Heroes and The Conduit come to mind. None of these were million sellers.