Federal and State Taxes still at Accepted Status

I filed my Taxes using Turbo Tax on Feb 7th and the Federal was accepted on the 13th and the State was accepted on 18th of February.  I'm just wondering what is taking them so long to go from Accepted to Approved and since it's all electronically done what else would they be checking for???  I'm just curious... does it just stay in limbo until about 21 days after you filed to get to approved??...