I think it's a reflection of Cosby's declining power in the industry (he is almost 80, after all) and a change in how society views sexual assault.
One of the accusers, on waiting 30 years to be believed:
http://www.washingtonpost.com/postev...ieve-my-story/
I do remember the stories that came out ten years ago (give or take) but that they didn't go anywhere.
It is interesting that there aren't a lot of people who have worked with him stepping forward to defend him. There's an anecdote in this link about the time he sucker-punched Tommy Smothers:
http://www.pajiba.com/think_pieces/a...l-behavior.php