This is definitely going to negatively impact their brand image among bourbon connoisseurs. But, does Maker's Mark even care? What percentage of bourbon sales would be to "bourbon connoioseurs"? I'd be willing to say that it's a pretty low figure.
The previous poster was correct. This is the "American way". Build a brand image based on quality, then dilute your product (in this case quite literally) to maximize profits and make up for it through established brand image, marketing, and consumer ignorance. You see it in all industries. Quite frankly, I think it's sad.