The key difference is the temperature mate, the steam mostly evaporates and a pressure washer doesnt especially at this time of year, also car engines being so much more compact makes it a lot harder to "stay away from the electrics" where exactly on a clio engine CAN you spray a jetwash and not be near electrics? And I disagree on the delicateness of the loom, the looms on these cars frequently go wrong due to water ingress even without a pressure clearner on the scene!
Knock sensor and oil level sender at the front, starter at the back, alternator on one side, temp sender and throttle body on the other side, coilpack and plugs on the top etc, there just arent any big areas worth spraying with a jet wash in the first place.
I just dont see what he is really going to gain my trying to pressure wash a couple of tiny parts of his engine, and then have to do the rest manually anyway, and the spray bouncing off the bits he does want to hit is still going to be travelling at speed when it bounces onto the bits he doesnt want to hit. Its just a generally bad idea as there is the potential to start off bits of the loom rotting, and in exchange for what thats actually useful?