I actually thought about this exact thing before I wrote my comment. What you forget is this is an adversarial situation you're dealing with. If it really mattered, nobody would leave it to a coin toss as to which way the staircases have to be. Much like in sports, every little edge counts. Yeah, it isn't chance that 70% of them are CW, but it also doesn't make sense that it's only 70%.
The proper comparison is not a 50% cointoss, which is how you might think about some elections, it's a 100% world where every castle maker would tell their apprentices about this important CW swordfighting idea, and people who forget this are castigated for building an obvious weakness into their design.
The only reason it would be somewhat lopsided, but not decisively, is if there was some mild reason why people preferred one over the other, which is what your numbers actually suggest. Something like the "easier to walk down" hypothesis might make sense here, where for instance the CCW staircases are accounted for by aesthetic considerations like symmetry.
The proper comparison is not a 50% cointoss, which is how you might think about some elections, it's a 100% world where every castle maker would tell their apprentices about this important CW swordfighting idea, and people who forget this are castigated for building an obvious weakness into their design.
The only reason it would be somewhat lopsided, but not decisively, is if there was some mild reason why people preferred one over the other, which is what your numbers actually suggest. Something like the "easier to walk down" hypothesis might make sense here, where for instance the CCW staircases are accounted for by aesthetic considerations like symmetry.