Then you find out only 2% of people played RB online, so it's no wonder that they were all expert players. Me, I don't want to work that hard to have fun. Hard guitar is what I play mostly.
I'm a mix of hard and expert, I just like to have fun. I also miss keys more than online. I think the problem with keys is that the difficulty creep wasn't as rewarding to power through as the other instruments. It's a lot less immersive than guitar or especially drums, imo.
I think Rock Band certainly has a hardcore niche but it's overarching theme is to be a fun party game, and I think Harmonix has accurately correlated that their most vocal fans are most of the same ones who play online.
It's important to cater to those people too but I'm sure they realize that if corners had to be cut, it's easier to provide an experience to make 90% of people satisfied on day 1 - build up some overall goodwill and offer instrument and DLC compatibility to the gamers to tide them over until some of their other desired features come into place. The music and instruments provide the overall backbone of the experience and all of that is there (keys aside) which is great.
I have a feeling that most hardcore rhythm gamers are entrenched in the worlds of Beatmania IIDX or pop'n music anyways, I know a lot of those players turn up their nose at Rock Band for not being hardcore enough for their skillsets, so high end Rock Band is in a weird spot where it's too daunting for most and not challenging enough for some.