The cynical, snarky view of the new "complaints office" in Afghanistan: Well, if you control only 31% of the country, you have some time on your hands.
Less snarky view: Karzai's office may need a few independent sources of information. Leaders in other counterinsurgency wars, such as Ramon Magsaysay during the Huk Rebellion, had similar programs, if for no other reason than to increase the appearance of government responses. (Magsaysay actually followed up on many of the complaints, however.)
Ultimately, any program like this depends on the power, influence, and energy of the leader in question.