At last, Mr Whedon himself has told the tale.
Basically, the Network and I had different ideas about what the tone of the show would be. They bought something somewhat different than what I was selling them, which is not that uncommon in this business. Their desires were not surprising: up the stakes, make the episodes more stand-alone, stop talking about relationships and cut to the chase. Oh, and add a chase. That you can cut to.Um, who did they think they had hired?
You know if you want to read Mr Whedon's ramblings. I will say in advance that they are long and, in the end, reassuring.