In a recent meeting, Nebraska Service Center has clarified why, some times, in cases of pending I-485 applications, USCIS approves AOS interchanging the applications of the derivative and principal applicant:
The news item and related documents are available here:
http://www.immigration.com/newslette...prmprocss.html
Please note, for now (June 2008), premium processing is only available if you meet ALL of the current requirements:
1. Your are currently on H-1;
2. Your H-1 status is expiring within 60 days when you apply for I-140 premium processing; and