Complex to develop, not play. We're talking about why a remake of Tetris that keeps the same basic formula but adds pretty 3D graphics and uses a Wii-mote might be less buggy than a huge, open-world game.
Again: you confuse "complexe" and "time consuming".
two things;
1) The game is not only about graphics. Even if the graphics are extremely complexe to build, and they are, that doesn't mean the game as a whole was complexe to design.
2) Simple systems are simple to develop. It is that simple (yes, pun intended).
edit: Yes i know the nature of the beast (sandbox) makes it complexe to code, but we are not talking about the same thing. When you say "complexe to develop", I think you actually mean "complexe to program". The developpement part is figuring the systems and building the gameplay, not about how to write lines of code. Even that is not complexe: like everything, it simply requires the programmer to know the code, and then he's off.