Among the most popular uses for stepper motors in robotics I’ve noticed that people use stepper motors in pairs.
Is it a safe assumption to say that this is true 90% of the time?
no that’s an assumption, not a safe one. And it’s a statistic too, even worse 
If you’re contemplating building a controller board, then often it makes sense to have multiple devices, and pairs do seem popular. But 3 could be an equally valid number. Or more. Check out the CNC and robotics forums for others who might have been down this path in the past.
I thought so. Thanks brett