The fact that at least in whiskey areas producers offer a range of proofs for the same brand must mean customers like the choice, but why? How do customers who realise there is a choice decide which one to buy, I wonder?

You raise an excellent question. My thoughts:

1) With VOB, the 100 proof version has a distinctive label. (Although clearly marked to those looking closely, I think the 86 and 90 could be more easily interchanged);

2) WT 101 vs. 80 is labeled clearly.

3) JD has not substanstially changed the label or bottle design in 30 years.

Is proof preference a product of marketing? I wonder. I feel that the VOB bottlings are pretty much equal, but I discovered them without the aid of marketing.

I have a strong preference for WT 101 VS. 80, but 101 is more aggressively marketed, in my opinion.

Furthermore, JD changed proof 2 times since I started drinking it, and I never noticed.