i think its about making it self validatable and auditable for his facebook credit system between his payment gate way and all his partners in the games industry(like zynga) and advertisers(like google)

simply to not have to employ auditors and security guards and able to pay his partners in a way they can verify funds easily and cheaply.

yes even in a closed system just the auditing/verifying element of blockchain tech can save on staffing costs.
after all mining pools dont need to employ accountants to verify tx balances. its all handled by code