Is there any android smartphone that is already rooted by default? Is there any android smartphone commercially available that is already rooted by default, so that no rooting procedure is required?
No, There is no phone with root access pre-built but there are phones like oneplus with cyanogen OS. 

I hope these links may help you reguarding this topic.

http://www.makeuseof.com/tag/why-doesnt-android-come-rooted/
http://www.androidauthority.com/sell-android-devices-already-flashe-119002/