The idea that if you just asked correctly no horse would ever say no is suggestive that they are good little robots, if you can just figure out their programming.
Sometimes horses say no. Sometimes it's because they hurt, and sometimes it's because, yes, they were not asked correctly.
And sometimes, because they are NOT little robots, it's because they just don't wanna.
It's up to the rider to figure out what exactly is going on, but I don't have a lot of respect for people who think a horse can never have or express an opinion.
I do sometimes call my horses names, in the same way my brothers and I will call each other names. I tend not to call other peoples' horses names, in the same way I try not to call non-family members names.