well, I don't think I would go so extreme as to say it doesn't matter, because it matters greatly. if you don't have enough power going in, you don't get the power coming out. so number of cells is extremely important. assuming the losses are 10-20%, which is typical, if we want a certain number of Watts out, we need to put in that extra 10-20% in. if we have a set number in mind, then we need a specific voltage to accomplish this. it's simple electricity math. so number of cells is important, or we don't get the Watts out that we need.
personally, I don't care about Watts, since it's not the most accurate unit of measure. it's a good indicator of what to expect, but it isn't perfect. I don't even care about Kg or lbs of thrust. I prefer the good old fashioned Newton.