Sorry, but I see no logic whatsoever in putting the 1 at the top. If I look at a keypad I look from the bottom, seeing first the 0, then the 1 and then the rest. To me that is logic.
For quite some time only adding machines had a keypad. Older ones lots of rows with the ones at the bottom and the nines at the top, the hand coming always from below. I've know people using only the 1 - 3 buttons, pushing the 3 3 times for a 9 (and they were faster than everyone else!) so they could leave their wrist on the table!
One thing is sure: when the first pushbutton phones came into existence the adding machine had been around quite some time. So the most logical explanation in the site you mentioned is speed, the same stupid reasen that got us the qwerty-layout.