They scramble them differently each time. There's this many different combinations for the cube:
8! X 3^7 X 12!/2 X 2^11 = 43,252,003,274,489,856,000 which is approximately forty-three quintillion.
So yes, some way that the solver is given the cube could make them do the cube in less moves, so it is the luck of the draw as to which cube you get.
Computers can solve it in a maximum of 20 moves, which is less than most humans can. If the cube was setup the same way each time, people would solve them the fastest route possible instead of having to solve a random cube.