Not sure if producers make the best band managers, but I do see the logic...

After all, they are the ones who often discover new talent; so doesn't it make good business sense for them to also offer services to develop it?

"As music sales drop, producers need to expand beyond their core business of making records," writes Beall. "It’s equally clear that managers and management companies are increasingly dominating the industry– they are taking the leadership position once held by the record labels.

 

 http://www.hypebot.com/hypebot/2008/08/the-producer-as.html