It looks as if Al-Diriyyah is likely to get a de/referral unless Saudi can successfully play the "only Arab nomination in 2010" card - I hope so!! See my reviewhttp://www.worldheritagesite.org/sites/t5086.html
I could imagine potential issues over conservation of much of the site and the nature of the restoration - both seemed problematic when I was there in 2002. But that was before Saudi had decided to go for WHS nomination and I wouldn't have thought that they would be short of money to cover all aspects in the best available way!
"The International Council on Monuments and Sites is now studying the third Saudi site, the historic Jeddah, which will be discussed during the next World Heritage Committee meeting in July 2011 in Bahrain. The Council had earlier expressed technical reservations about Al Diriiya, but the Saudi permanent representative is continuing his efforts to have Al Diriiya
(From Khaleej Times)
This all seems directed at preparing readers for a delay.