Cutting away a lot with a router is a slow, noisy and dusty process. Less work to just glue together the channels out of smaller pieces of wood. Also, that way you can take individual pipes out and tweak them (called voicing).
Another thing to be wary of -- pipes too close together sometimes pull together in pitch if both are played at the same time.
Another thing to be wary of -- pipes too close together sometimes pull together in pitch if both are played at the same time.