Yeah we do too (go more than 40nm of route) of course but I have never seen anyone go 40 miles downwind of a single cell that reaches 40,000'. Maybe it is because almost all the weather I have had to deal with is crossing the equator, india during their foul weather season or typhoons and going 40nm downwind is usually not possible as would put you into more crap. Like I said it is hard to give one rule that fits all situations and until you start doing it and watching what others do it is hard to learn what to do from a book as all situations are different. I am sure those huge tornado producing storms in the states require a wider berth but as I don't fly there I don't have the experience to comment as it is hard to know until you have sat there watching someone experienced doing it.