I've noticed that, too. Look at any '54 GMC ad, all of the ones I have seen have the '47-'53 style steering wheel. My best guess is that they did the advertising and the manuals early enough that they didn't have any round-button steering wheels yet. Otherwise, the steering wheel change was decided at the last minute.
My '54 GMC panel was the 42nd truck off the line in St. Louis that year, and it has the original round-button steering wheel, so I would be very surprised if any production trucks were built with the older wheel.
On the same subject, the owner's manual shows the '47-'53 style headlight switch knob.
Of course, the Kook is the GMC guru, I'm sure he'll correct me if I am wrong. :p
