After gaming for the past +30 years, I see LBP as hardcore. Why? It's a work of art. It's style, physics, aesthetics, etc. is a breath of fresh air for the platformer genre. There is a sort of depth that LBP has that's indescribable. And I don't expect every one to like platformers just like some are not into FPS. Most of the mainstream are into what's familiar and shallow. Now, I'm not calling games that have done financially well as shallow because there is a bigger picture here. You take an FPS that has depth such as deep storyline, great characters, and detailed customizations. But what's probably attracting the mainstream are naturalist graphics and familiar subject matters (such as war). The mainstream typically goes with something familiar to them as a catalyst while the non-mainstream (what I call hardcore) looks more into what a game has to offer. LBP is a great platformer. About sales, I don't know how "HUGE" it will be, but most of the games I own are not the "BIG" hyped sellers. As long as sales are good enough to support a quality sequel while continuing to keep the market with different and good idea to keep pushing the market then all is good.
Hackers are poor nerds who don't wash.