Topic: Married for less than 2 years but received COA:F26 (10 years green card)

Hi, My wife is a LPR and we are married for around 13 months now (as of Oct 2013). I am on F1 visa. Last week we had Adjustment of Status interview and today we received the welcome letter with COA as F26 and I797 says that I will be getting 10 years green card. Is this a mistake on the part of the USCIS or do they give 10 years based on individual scenarios? What do I have to do now? Please advice. Thanks