It's kind of like buying an airline ticket that combines two different fare bases - say, getting a non-refundable discount fare for an outbound flight but due to peak travel being stuck paying full "Y", which is refundable, on the return.

Your point about confusing cancel policies is well-taken. Many "special" hotel rates - not just Marriott's - have the "cancel by 6PM date of arrival" rule written in as boilerplate text, but also include another note about the reservation being non-refundable or non-changeable. When you combine two different rates it only compounds the problem. Maybe having 3 different reservations would have been less confusing, but then you're trading ambiguous rules for other kinds of administrative overhead. I honestly don't know what to do about this. If you asked the travel industry to come up with a solution to these kinds of problems they'd probably just apply the most restrictive rule to the entire stay, which isn't fair either.