orgopete, I'm still not sure I completely understand your complaint--primarily because it seems you use different definitions of inductive effect and resonance than I'm used to. I take inductive effect to be the disturbance of electron density of an atom which is propagated through the sigma bond framework. And I take the resonance to be the disturbance or delocalization of electron density through a conjugated pi system (or adjacent p orbitals, more generally). Pi electron delocalization stabilizes anions because a dispersed negative charge is a lower energy state of affairs than a concentrated, localized negative charge. Anyway, I take you to be claiming that for any example of acidity where inductive and resonance explanations can be given, the inductive explanation is entirely sufficient, and so resonance is superfluous in explaining acidity. Otherwise, I thought you might be claiming that inductive effects are always stronger than resonance effects (assuming it affects acidity). Both are strong claims, and I'm not sure if either accurately characterizes your position, but assuming they do, I believe I have at least one exception to such claims.
Take the example of ascorbic acid. It has two hydroxyl groups on the ring. The interesting thing about the acidity of these two hydroxyl groups is that the hydroxyl group ("A"--the one attached to the carbon alpha to the carbonyl) which one would assume would have feel the greatest cumulative inductive effect is actually less acidic (pKa 11.57) than the other hydroxyl group ("B", pKa 4.17). This can be explained by the fact that resonance structures can be drawn for the conjugate base of hydroxyl "B" which delocalize the charge on oxygen, but not so for hydroxyl "A." To me this example demonstrates that resonance stabilization can influence acidity and that in at least some cases resonance effects are stronger than inductive effects. Why couldn't resonance be of equal or greater importance than inductive effect for the acidity of carboxylate anions, etc.?
I think we need a physical organic chemist to put some numbers to the inductive effect and resonance effect as applied to particular cases in order to sort all this out, rather than resorting to a qualitative discussion of acidity trends.
[reference for ascorbic acid pKas: http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/special2.htm
Okay, try this, acetaldehyde and its enol (1-hydroxyethylene). If resonance determines acidity (they have the same resonance structure), why is the aldehyde more stable?
For those of you who disagree with me, please re-read my post. Note how many instances of inductive effects I give. Then think about it. If you think I am wrong, then let me tell you acetaldehyde and its enol have different pKa values. The enol is much lower. If the acidity of a carboxylic acid is determined by the resonance stability of the anion, then acetaldehyde and its enol ether should have the same pKa as they have the same anion.
One explanation for the difference in acidity could be that while the resonance stabilization is equal for both the inductive effect is greater for hydroxyethylene, so it is more acidic. This would show that resonance alone
doesn't determine acidity--but I don't think anybody even claimed that. So the example seems to be beside the point. However, there is something
wrong with the resonance effects explanation that people sometimes give. As my Solomons and Fryhle Ochem book tells me, resonance stabilization isn't determined solely by the conjugate base resonance hybrid, rather it is determined by the difference
in energy between the resonance hybrid of the protonated acid form and the resonance hybrid of the deprotonated form. Thus, the difference in acidity of acetaldehyde and hydroxyethylene could also be explained by the likely fact that the conjugate bases of acetaldehyde and hydroxyethylene actually don't have the same resonance stabilization energy.
My Solomons book also tells me this article has more info on the inductive/resonance debate: Bordwell, F. G.; Satish, A. V. J. Am. Chem. Soc. 1994, 116
, 8885-8889. I don't have access to it, so I can't relate its contents.