Originally Posted by
orbitmic
Agree they should... but they don't - so you are right, it is not the possibility to pay for an upgrade but the possibility to pay not to be downgraded!
AFAIK,on Delta, no first only First/business: Delta, on US flights, sells only First/business tickets with BC "F" or "P" for flex and "A" for restricted. (150% EQM). RTW on Delta in business is with BC "C" (175%EQM), available only on intercontinental flights, not domestic.
But you are right, with this RTW rule, you pay to do not be downgraded...