That's correct. The only thing you're "waitlisting" for is the complimentary status-based upgrade, and even then it's a request, not really a waitlist.

After an upgrade is requested, the system will attempt to upgrade you once you are eligible for the upgrade (dependent on your FF tier status and what class of service your ticket is booked in), and if no -U- class is available at that time THEN it will "sell" a waitlisted -U- segment.

That waitlist then clears when -U- becomes available, but the system stops clearing waitlisted segments once we're within 36 hours of departure.