I once reported something that my boss said to the heads of the company. They sent HR in to take care of it instead. My boss said, "I could get fired for what you said I did." He didn't deny it, just that I could cause him to get fired. I said, "Yeah!" or something similar.
The company's response? I was to talk to my boss first next time before going above his head. For something he did that was (I think) illegal, and clearly not okay. I assume that was so he could sweep it under the rug.
That year, I didn't get a raise, when I normally got rather large raises. I went somewhere else 6 months later and immediately earned 40% more.
I'm not at all surprised that 75% say they faced retaliation.