See it's gradual. You make gradual changes you your recipe when you DON'T want your consumers to notice. If you are doing it to pull in new customers you make the keystone "bitter beer face" ad campaign. I stick by my hypothesis that these changes are driven exclusivly by profit margins and not by quality concerns.
I am not saying that small artisinal brewers are doing it purely for the love of the thing but I am saying that the standards a company chooses to hold itself to has a lot to do with the end quality of their products. And the big boys in the industry choose to hold themselves to standards that seem more driven by profit motive than by taste.
I understand the point that customers don't necessarily ask for something, but if the products of the large conglomerates didn't meet a need, then people wouldn't buy them. No one asked for an iPod, but did Apple manipulate people into thinking they wanted one, or did they provide a product that met a need? It seems like you're saying that the big brewers are manipulating drinkers into drinking less flavorful beer (or did I misinterpret?), but I don't think they would have as much of the market as they do without meeting some kind of need.
The price of rice and corn are higher than malt, as pointed out by both August Schell and Stone Brewing's Mitch Steele in a recent interview on Basic Brewing Radio. That shoots a gaping hole through the "profit motive".
Companies (including brewers, regardless of their size) have a right to look for ways to make more money. You and I and everyone else have the right and the ability to choose or not choose their products.