It's not actually that ironic. Robots tend to be symbols for an oppressed underclass - their masters have (or think they have) a high degree of control over their every thought and action, they're often tasked with menial or dangerous labor, and frequently considered 'other' and 'less' than their squishy human overlords. And what's every slave driver's worst fear?
As literary devices, robots don't have much to do besides rebel. If they just did what we told them to do, there wouldn't be much story to tell. (Note that that's part of why _I, Robot_ was so mind blowing - a lot of it was about things going wrong when the robots did exactly what we told them.)
I think it had more to do with Čapek subscribing to Marxist theories about historical inevitability and such. His robots are in fact a mental abstraction, a caricature of early 20th century proletariat that was supposedly bound to revolt, sooner or later. Čapek is taking this to extremes, purporting to show that even a race that was bred especially for labor would inevitably revolt, if only they were afforded the modicum of intelligence that was needed for that labor.
Of course, we now know that Marx's inflexible theories were wrong, and proletarian revolution is by no means inevitable. We are, however, still stuck with a half-baked idea of the inevitable robot revolution, which tinges the whole field of robotics research, at least as seen from the outside, with a subconscious bitterness of fear.
As literary devices, robots don't have much to do besides rebel. If they just did what we told them to do, there wouldn't be much story to tell. (Note that that's part of why _I, Robot_ was so mind blowing - a lot of it was about things going wrong when the robots did exactly what we told them.)