prof. sahib is talking about the sunni inaction in terms of writings books. the second half of this post http://www.sunniport.com/masabih/showpost.php?p=4893&postcount=35 addresses some reasons for this.
http://www.youtube.com/watch?v=bASqMoLU2NM http://www.youtube.com/watch?v=sJ_Halw0Zec http://www.youtube.com/watch?v=DVhKamFpwCs http://www.youtube.com/watch?v=AqMQ_2iThF4