More like, this is the package Apple chooses to sell as a product, and the OS is an inherent part of that package. If you don't like the package, you can simply choose to purchase an alternate product.
That's how "choice" works in the real world pal. And that's the beauty of being a consumer. You buy products if you like them, you buy different products if you don't. The OS is part of the package, and iOS 7 is part of the product that Apple is selling. By using an Apple product you agreed to an EULA that stated Apple may alter or change the software as they see fit. Also, you proceeded with the update, it didn't install on it own, it only downloads itself.
And no, usage would not drop down to 40% if given the opportunity to downgrade. Just because you haters make the most noise doesn't mean you speak for the majority. You're a vocal minority. Most people are happily using 7, some probably indifferent, some loving it, others not as much. But we would see massive return rates and low customer satisfaction scores if half of customers HATED it. But guess what, that's not happening. Turns out Apple can't keep the damn products on store shelves, and people are enjoying them.
Get it? You're a vocal minority. Either get over it, or move on to a different platform. Nobody will miss you guys.