The Batgirl issue is its own thing, which doesn't fit the scenario as it's portrayed. It is a useful point that many of the characters in mainstream comics have other issues besides a strict lack of audience or lack of quality, but in a discussion of originality in mainstream books, it's not quite germane.
My point more or less stands: there is a sizable audience of mainstream comic book fans who pick up a book every month regardless of its quality, whether it's to enjoy bitching about it without guilt or because they don't want to break up the run or simply because they always have. They reward the company with sales independently of the company's actual commitment to quality in the product.
You can see this cycle perpetuate itself in pretty much all areas of geek culture, really. The comfortable and familiar gets rewarded; the new and potentially groundbreaking gets ignored.