Wherein the code is it stated that commercial office building receptacle circuits are 20 amp, why can't 14ga wire be run and place receptacles on 15 amp circuits?
It is a design issue. The reality is that office type settings will have multiple computers, printers, fax machines, etc. all plugged into whatever is close. 20 ampere circuits and fewer receptacles per circuit have a better chance of providing good performance for the customer.