No, not true. There are two pay-for-upgrade mechanisms. One is a buy-up-to-F program, which offers customers the ability to "buy up" to the lowest F fare without a change fee (which could be a Y/B/M-up fare for elites). This is offered even when there are elite pax on the upgrade standby list. (And this books the customer into Z, etc. fare classes.)

The other program is a day-of-departure upgrade program. Under this program, a customer is offered an upgrade to F for a nominal fee only if there are more F seats than there are elites awaiting an upgrade. This is analogous to a non-elite passenger buying an elite upgrade because this books the customer into R class.