The Apatow phenomenon is similar to the Vince Vaughn phenomenon.
In both cases, they had a string of Medium-Funny projects, found themselves in the spotlight, then got real itchy at the idea of relinquishing the spotlight and accordingly started saying "Yes please!" to any mediocre idea pitched to them. Most moviegoers start to recognize when quantity begins to compensate for quality. John isn't the first person to suggest that FSM would burst the Apatow bubble.
(For the record, I haven't seen FSM, but the trailers did make it seem pretty fluffy)