I think you're seeing some bias just because scopes and power supplies are so prevalent, though there are a few others that are common and maybe don't feel like they fail as much.
But RF equipment has some kind of failure frequently, often due to misuse (easier to do, more risky conditions, more sensitive inputs/outputs, etc.), but also just to aging. Amplifier stages often run hot and just by leaving it on for long enough, you see a good bit of older RF gear which just needs an amplifier somewhere in the chain replaced, but you'll see mechanical failures of attenuators and things too. Then again, some of this may be the bias that fewer people are attempting to actually repair them.
As someone who's seen a lot of faults... I don't think there's a class of instrument that stands out as more likely to fail. There are bad designs, commonly failing components or elements, and equipment/interfaces that are more likely to be abused, but on the whole things are much more similar in terms of non-user-error faults.