The word "simply" does not belong in the same sentence with "implement ACH".

Signed,

Someone who worked on ACH for nine years.

ps: I'm pretty sure they're trying to do just that. But you have to consider just how incredibly difficult ACH is - not just from a coding perspective, but from a regulatory perspective. Banking and accounting legal entities need created.

pps: ADP knows good and well that Zenefits is working on their own ACH implementation with their buckets of cash. This is a preemptive strike.