You're right and I thought about that as I was writing my previous post but forgot to mention it. On the distillery tasting panels, even, they do dilute with room temperature water (never ice) to experience the full range of the whiskey's taste. Of course, they're also starting with barrel proof, so they have to dilute to reach the proposed bottling proof. This is how they arrive at the proof we consumers will experience when drinking "neat."
That isn't to say that the distiller is the sole person who decides the release proof. It's also a business decision. Several distillers have told me about products they wanted to sell at higher proof, but the "bean counters" wouldn't let them.