The popularity, I think, of RAID is derived from installation types around the world and the people that are setting up these new databases. Mom and Pop shops may not have the money to buy RAID 10 and RAID 5 may be pressing their budget but it is the best option for them. It also depends on type of database and volume of transactions as to whether it is an appropriate choice. Not every database needs to be on RAID 10 - it just doesn't make sense for the cost versus transaction volume in many cases.