I think the key phrase here is "protective device rating." I also noticed that the code section says if such a rating is marked on the device, then it has to be followed. So if I look at a dishwasher's nameplate and see, for example, 9.6 amps, is that merely the rating of the dishwasher, or the "protective device rating" of it? That "if" makes me think it's not something that will always be on a nameplate.
On the more practical side, if I wire up a multiwire circuit/receptacle for the dishwasher and disposal, I often have no idea what the appliances are rated for when I do the wiring because the homeowner frequently doesn't decide on a specific model until later in the process. I don't think it will fly if I tell someone that I'm only going to install for 15A unless they prove to me that the appliances will allow a bigger circuit.
I've done these dual 20s for a while now, and none of the inspectors I've dealt with has ever said a word to me about it.