Exactly. If someone came up with a business plan to sell hearing aids of comparable quality at half the price, the insurance companies would push customers to use that vendor. Those insurers who did so could offer lower premiums and thereby attract more customers (or keep their current ones). The fact that this hasn't happened suggests that it's not so easy to sell hearing aids for less, contrary to what many commenters are saying.
I sort of do. I rely on Outlook's holidays to know, for example, whether to expect banks and government offices to be open or when my trash should be put out a day later than usual. My employer (a university) provides an.ics calendar of its schedule--it follows some official holidays but not others. So I need to be aware of both, and generally assume that Outlook's holidays are reliable (though an unusual change like this would likely have been well-publicized).