Is that an actual law, or is it just that some implementations of the pattern are deficient? My impression is that the actor model was originally envisioned as being applied to a machine with hundreds or thousands of processors.
I think it'd be harder to make them run serially than concurrently, and of negative benefit.
Unless OP is saying this is some "rule" of being an Hewitt "Actor" in which case I'd call that somewhat arbitrary and unnecessary.
