Part of the problem with this discussion is that meaningless terms like 'tonal range' and 'tonal scale' are being thrown around as if they had some sort of quantifiable meaning. Jorge is exactly right in his previous posts. The differences between the processes have to do with the reflective density difference between platinum and silver gelatin. Azo/Amidol does not have a greater reflective density difference than any other glossy finish silver gelatin paper. Dmax for all of these range from 1.9-(2.1 in some cases.)
Because of the matte finish that handcoated platinum prints have by necessity, the maximum reflective density is anywhere from 1.3-1.5
(In a *well made* print. As an aside, you will see many basically crappy platinum prints floating around made by some photographers that have some serious technical problems in basic technique. Do not assume you know what a good platinum prints looks like until you have seen one done by a Kerik, a Dick Arentz, a Stan Klimek, or a Stuart Melvin. )
But back to the reflective density thing. If you get a silver gelatin paper with a ^matte^ finish, guess what? The maximum reflective density of a maximum black is about 1.5 - same as platinum/palladium. As Dick Arentz points out by way of Minor White, what really matters is the 'convincing' black. If the paper is delivering a reflective density that appears maximally black to the viewer, he or she won't give a rat's ass whether the Dmax is 1.5 or 1.9. The thing that makes a print 'sing' ,or not, is the gradation between the infinite steps of tone (yes, more than 256, you photoshop users), and how this gradation reflects the actual brightness differences that were present in the original scene.
If you print (with good technique, again) a step wedge on Azo and a step wedge on platinum/palladium, and plot the results, you will notice that the high negative densities on platinum/palladium stretch out into a very long toe. The highlight gradation is very delicate. At the other end of the plotted curve, you will immediately see that the shadow values are also somewhat compressed and have a lower slope (e.g. lower contrast) than the relatively straight line area between ^print^ zones 7 and 4.
The Azo wedge will show an amazingly straight line response, with very little toe and shoulder on the curve. I've done this exercise, and its interesting. Azo/Amidol is strikingly different than Azo/Dektol in its curve shape. The point that Jorge makes is relevant, though: Just because platinum and Azo/Amidol require a density range of 1.4 to completely 'fill up' the print density range just means that you have to have more contrast in the negative to begin with. If you choose to use a process that has a print exposure scale of 1.0 to completely fill up the reflective density range of the print, you can tailor your negative exposure and development to give you just that result.
What does all this mean? I think it means we are technologically capable of producing stunning prints using either process. It just depends on what 'look' you like. Give me the process, and the real life reflective values you want to capture on the final print, and I can make you a negative that will fit the process. It also means that we have the technology at our fingertips to produce trivial, shoddy dreck. Taste, discrimination, and esthetic sensibility will go a heck of lot further than chemistry in producing a fine print. Understanding how the process behaves is only useful if you have a real vision of what you want to achieve.
This whole thing is similar to an argument over "which is better, red wine or white wine?" Believe me, there are some crappy wines of both types, and it seems like it might be more relevant to discuss "which is a better white wine" or "which is a better red wine". And don't ask somebody who hates sweet white wines to give you useful assessment of a bottle of Chateau D'Yquem, or conversely, ask a red wine hater to give you any useful information on bottle of Lafite Rothschild. And my red/white wine analogy is good, I think, in that there are some people who like one or the other, and some lucky souls who can taste and appreciate both.
So drink up and go make some art.