Sorry, I am correcting myself:
According to this article the FIVB World Tour consist of all GrandSlam events plus the World Championship, but for the World Ranking the points earned on FIVB Opens also counts.
"The 2013 FIVB Beach Volleyball World Tour is comprised of 10 Grand Slam events and the 2013 FIVB Beach Volleyball World Championships. Not part of the World Tour but still counting towards the FIVB World Rankings, the FIVB yearly calendar also includes eight Open events."
I really hope this is the final version