Re: downrod splices.
OK. . .I've got two more.
1. Wildman, I stopped by a local home center, kittycorner from the Big Orange, to see if I could find a second type of wire extension kit. I found a kit from the Republic of China, no-name, and the instructions said essentially the same thing that you posted. Here's what struck me. The instructions refer to "codes" as the apparent reason to not "splice in the conduit". If the "codes" are the NEC, the NEC doesn't extend past the fixed wiring of the building. The UL White Book says the paddlefan (GPRT) begins at the part that attaches to the jbox. The downrod is part of GPRT and, therefore, can't have the code regulate it. . .that already has happened when the fan went through UL. If there are other "codes" that do apply, I want to learn about them, but it seems to me UL approved the #18 as part of the GPRT assembly.
2. Many, not all, downrods are secured by thick pins to prevent the motor from eventually unthreading the downrod. The pin runs straight through the downrod, greatly reducing the cross sectional area inside the rod. The commodity fan has 1/2" pipe, made smaller by the pin, and 344.20(A) tells us that the minimum size of RMC allowed is 1/2". Of course, the effective cross section of the pipe can be smaller if it is not regulated by the NEC.