Don't get me wrong, Paizo puts out some outstanding work, and for a few years I was a subscriber to their Adventure Paths, but would they be as successful selling adventures if they had not had the exposure they got from publishing Dungeon and Dragon magazines?
The position that adventures sell well for Paizo, does not automagically translate to adventures sell well for everyone that puts out adventures, or even very good adventures. The exposure to the market is in part what made Paizo successful.
Of course, the exposure from Dungeon & Dragon helped. It's also irrelevant. Didn't WotC stand upon the shoulders of 1st & 2nd edition D&D when they released 3e?
Looking at TSR, 1e grew the company & the mismanagement during the 2e days killed it. What came before was no indicator of future success.
The point the OP is making is that, regardless of the circumstances that set up the situation, Paizo appears to be disproving the "accepted truth" that modules don't sell.
Personally, I chalk the "modules don't sell" belief to subjective analysis. True, modules sell to a smaller market (DMs vs. players). They cost less and therefore earn less profit. So for a company like WotC, it doesn't make business sense for them to invest in that vs. rulebooks. For a smaller company like Paizo, it might be a viable business model.
I think that, in typical WotC fashion, when those statements were made they were wisely trying to make their point and move on rather than get ensnared in a debate. My personal belief is the more accurate statement is "Modules don't sell enough for us (WotC) to expend resources on them." It's apparently held true for other companies as well.
Clearly, Paizo disagrees but more importantly, they're showing the lie in the statement. Can every publisher produce Paizo-quality modules? Obviously, no. But is there a market for high-quality modules? Clearly, yes.