Adjustment of Status - I-485

My wife (US citizen) and I (beneficiary) attended the I 485 interview today and overall we felt it was a positive experience. The IO started off by making us taking the oath to tell the truth, and began to proceed by asking for IDs, original birth certificates, marriage certificate. While she was reviewing these documents she began asking us how we met, who proposed and then asked us if the address on file is still current. We had bought a house soon after filing for AOS so we gave her the title, mortgage monthly statements, homeowners insurance, joint bank accounts. She then asked the wife to write notes on some pictures that we want to leave with her and proceeded to ask us the Yes/No questions. She also took the new medical I 693 and said it was good that we brought an updated one since the old one had expired. She however didn't ask for my EAD, previous Visa approvals or anything like that.

Based on several other people's experiences since we had all the documents and evidence I was hoping that we would get approved on the spot but it was a bit disappointing when she printed out a sheet that said we will review and do not need further documentation from you at this time. She said to check online for the status either tomorrow or Monday. I have been checking the online status nearly every 30 minutes and only thing that has changed so far is the status from case has been scheduled for an interview to interview has been completed and file is under review.

My question is is there a reason that the file is under review and status didn't directly change to approved? Please comment with your experience as this is beginning to stress me out.