No one says this. Everyone – the fans and the creators – admit that the show dragged in the second and third season because the producers knew what their endpoint was but didn’t know how long they were going to have to get there. You may think you’ve uncovered a big conspiracy, but everyone involved admits it.
–Cliffy
I seem to remember ABC actually wanted more episodes and the creators worked them down to 100.
I’ve never watched the show (other than randomly catching part of one episode), but based on the plot summaries above I’m going to take a stab at the ultimate explanation of everything:
Aliens did it.
I mean, there has to be someone responsible, or else the punchline is “The island is magic for no good reason.” Given all the crazy stuff going on, it has to be someone with the power to do basically anything. That could be either aliens or God . . . and God is too implausible. 
Shouldn’t that be 108?
ETA: tim314, I’m not positive about this but I think the creators have absolutely ruled out the “answer” being either aliens, they’re all dead and in purgatory, or it’s all a dream. It seems very likely headed toward a science/God hybrid, as right now they are heavily into quantum physics (or at least a network drama version thereof).