I data-mined AMEX approval stats via whogavemecredit. Here are the score ranges of approvals. The range is all over the place and they don't appear to have a particular score heirarchy for their products (anywhere in the high 500s to low 600s can be a starting point for any card). With the exception of Centurion, Simply Cash, and possibly Platinum. Interesting data, anyway.
AMEX Blue: 583-777 CL range: $300-$25,000
AMEX Centurion: 782-821 CL range: $100,000-$10,000,000 (question the veracity of this CL data)
Amex Clear: 592-770 CL Range: $1,000-13,000
Amex Costco TE: 613-800 CL Range: $1,200-$22,000
Amex DELTA Skymiles: 557-745 CL Range: $1,000-$13,800 (average CL is $2,000)
AMEX Gold: 601-755 (No set limit)
Amex Gold Rewards Plus 643-806 (No set limit)
Amex Green: 526-786 (No set limit)
Amex Hilton: 602-799 (2,500-20,000)
Amex Platinum: 651-785 (no set limit)
Amex Simply Cash: 802 (13,000)
Amex Zync: 602-770 (No set limit)
These are all reported as EX scores. Note that there is no guarantee people entered true FICO scores. Note that these stats don't include a large number of approvals that didn't specify a credit score in the EX column.
On average, there were more instances of approvals reported than denials (Approximately 500 Approvals vs. 400 Denials). This could be due to the fact that many people would be more inclined to report success stories than non-successes, or it could be a true reflection of approval: denial ratios.
Locking this thread. There is an identical post here: http://ficoforums.myfico.com/t5/Credit-Cards/Pre-Approve-AMEX/m-p/887990#M258339.