These "really slow" parts are actually tested and built for much more extreme conditions. For microchips that go into satelites, you even have hand-checked chips that go through a very long (and costly compared to something like a Pi) testing process. Multiply this by all the eletrical components, and you got yourself a lot of things to check.
Put your Raspberry Pi next to a car motor, and it's pretty likely(1) a part will fail in the heat and grime conditions.
(1) actually, I'm not sure about the likelihood, but there's no assurance that it will be fine