You have to consider it at the stage of peak torque. Like when the big guy stands up and both pushes and pulls with both feet. The spokes will see the full measure of that moment and that "worst case" is what they need to be able to withstand. They need to be able to withstand this force even though it's only present for 4 or 5 cranks. That's still a significant time and the spokes, indeed EVERY component in the wheel has to be able to withstand these peak forces. It's not about the average.

Danno, those are some good numbers but let's back up a little and look at your final analysis.

I'm with you up to the final total pulling force of 147 kg and that it being split between 16 pulling spokes for a linear TANGENTIAL PULL AT THE SPOKE HOLE OF 9.2 Kg. But that's where it breaks down. From there you have to consider the direction the spokes are angled at to determine the tensile load increase in the spoke. For a true tangential spoke the added tension in the spoke is at 9.2 kg. But as the angle of the spoke changes towards radial you need to get the sins and cosines out and figure out the difference. And when the spoke is not directly in line with the force there is a mechanical leverage of forces that increases the tension in the spoke to a value higher than it is when the spoke is in line with the force. Your otherwise fine set of data doesn't take that final factor into account.

And since my mind is awake now I was able to do up this vector analysis. Note that the angle isn't even close to radial in the second diagram but you can see how as the spoke angle approaches the true radial how the force in the spoke will multiply rapidly to extreme values. In fact if the spokes did not have the ability to stretch at all then a truly laced radial wheel would see the increase in spoke tension hit infinity. In real life a radial laced rear wheel would defect to some angle (as in wind up) and allow the spokes to come to an angle where they would generate the required triangle of forces. But the leverage on such a spoke at this very small angle would result in HUGE increases in tension that are way beyond what even the static tension of the spoke is. I think at that point you'd see either the spokes fail or the hub flange fail.

And this is why a disc brake or rear wheel should not be done in a full radial lacing.

EDIT- for the heck of it I reduced the spoke angle to 5 degrees from radial and 2.5 degrees. The resultant spoke tension increases at that point were 105 kgs and 210 kgs. At 2.5 degrees we're probably looking at an angle that would typically occur when our strong rider wound up the wheel and stretched the spokes from the true radial angle. I can only see very bad things occuring from such a situation.