There's sharing, and taking. A very fine line. Don't confuse yourself.
There's a reason you can't get legal protection on "A world made from blocks". To call minecraft idea-theft is patently ridiculous - since when was seeing something you liked, and using a few elements from that, in any way a bad thing? We all do it about everything, inherently and subconsciously. While I'm sure you're full to the brim of entirely original video game ideas that don't take place in worlds with any similar elements to any other world, played in a way nobody else has ever thought of, with truly unique and original characters, most people are not, and thus using ideas that you like and mixing them in a new way is quite good too. If we'd never been able to do that, we'd still be in the stone age, scientific research has always relied on the work of those who came before, but with new ideas and methods.
Fortresscraft, on the other hand, is a clone of minecraft. That's the design document - what the guy making it was aiming to achieve. Now, ordinarily, that'd be fine, I can get behind that, so long as you begin to have your own take on it - but when you act like a total jerk, release heavily substandard products *and* charge more than the thing you're trying to emulate (As seems likely with many chapters at $3 a pop), then no, I can't get behind that.