Delta App Updates

After I upgraded to 6.1.3( I think it's this version), I realised that app updates are super-fast. Updating FIFA 13 used to take forever( seemed like they were downloading the entire game) and recently it was updated in a matter of dozens of seconds! But I know that iOS has not implemented delta updates for third-party apps, so it's kinda confusing, although I definitely love it. Are you guys experiencing this also?