I don't actually think there's any need to not ground anything. But some designers have very... various ways of causing problems with their ideas of grounding.
Correct, there are tons of super sensitive equipment mounted on planes or satelites which are obviously not grounded but still work Grounding is only for safety and is something that can drive crazy even the most patient person. For those patient ones, here is a nice presentation clearly stating what is what [long read alert]
Grounding, bounding and hum (PDF)
For those with more technical ambitions, the bible of the subject: "Grounding and shielding techniques" Ralph Morrison
Cheers,