Do you have evidence that UA policy is "more generous" than required?
In addition to what is mentioned above, it is more generous compared with this requirement from the DOT:
allowing reservations to be held at the quoted fare without payment, or cancelled without penalty, for at least twenty-four hours after the reservation is made if the reservation is made one week or more prior to a flight’s departure date.
UA doesn't apply the 1-week threshold here - you can book a flight for tomorrow and cancel within 24 hours without penalty.
The key point in this policy (and how UA interprets it) is when the reservation is made. If you change a reservation, you still use the same booking reference from the original reservation, and you inherit several of the same conditions from the original booking - must be the same passenger, some domestic vs. international restrictions, etc. It isn't the same as putting cash towards a new reservation - you are changing the original one.