Another function of i-VTEC is the reduction of pumping loss. Basically it's a work-around to avoid turbulent airflow recirculation forming through the narrow gap of a partially open throttle valve.
Instead of partially opening the throttle valve at low speeds, the drive by wire opens it completely, or at least opens it far more than a conventional throttle valve. It, in effect allows free flow of air / fuel into the cylinder. In order to control how much fuel is burnt, the valve timing on the cylinder is delayed on the compression stroke. It literally sucks in a full cylinder-load of fuel/air and then squirts some of it back out, depending on throttle position, before combustion.
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