Well, the explanation is probably that I've been taken in by a meme. I should have added a disclaimer that I've not actually played infiniminer a good deal earlier in the thread, and my feeling that Minecraft was derivative was almost entirely based on its timing, visual similarity, and my understanding that the basic mechanic (digging through voxel based terrain) was the same.
An additional factor that made me extra-specially susceptible to this meme is that when I played minecraft, I immediately thought it was essentially a dumbed-down version of dwarf fortress with better graphics. What I saw at the time as the basic innovation - which I think is still what makes dwarf fortress exceptional, is a game that uses a tiling or cubic grid to allow for real creative play, with an attendant focus on mining, survival, and craft.
I don't think Star Wars is a rip-off of star trek, but it absolutely is and was always intended as a derivative work. All the ideas and content was developed in earlier sci-fi. Star Wars was an interesting contribution in terms of execution - and that's exactly why I like it. It had genuinely new ideas about set design and special effects. Minecraft, on the other hand, has no new ideas I can think of.
I still think it's a good game - and I'm very happy that when my kid hits the age where they wanna play games, I can point them to Minecraft and be pretty certain they're not going to be loading naked kidnapped people into a sausage factory (I played GTA2 when I was a kid), or squashing people with tanks, or irradiating them until they turn into mush. I mean, I guess they'll do those things at some point to, but it's nice that there's an actual honest-to-goodness kids game out there that doesn't suck.