You're right and it's very weird how Marvel and DC do this. They want to see big pre-orders of issue #1 and that's the biggest factor on whether an ongoing continues past its initial arc, whether a mini could get a sequel, or whether the main character(s) of the series gets more spotlight. If the book hits that mark then they'll start looking at overall sales but pre-orders of issue #1 make the loudest noise to the big 2.