The thing that makes the 24 hour after booking item different than some of the other examples is that is a legal requirement (if the booking is made more than 7 days in advance). While United has the right to cancel a person's mileage plus account for any reason, it would raise quite a bit of questions if it would happen because of someone exercising (perhaps abusing, which I don't think the OP is doing) a right governed by a federal regulation, as opposed to abusing airline policy on refundable tickets and such.