Just in the spirit of correctness, Smith was never set to direct Superman. He was asked to write a draft. It never got to the point of being serious.

I think with any big name adaptation, the studios want to cover all the bases, as far as story and price goes. FF got a rewrite because it was too expensive to make. Batman went through a few story ideas (Worlds Greatest with Wolfgang Peterson attached, Year One with Aronofsky) before getting to the current one. Watchmen almost got greenlit with Paul Greengrass directing, before Paramount went cost cutting.

Fact is, film deals change all the time. We just hear about it more because of the internet.