flashware if you look at the Wiki on this thread, which is probably the most accurate description available, you will see
"Paid-for STPC is only available:
For booking classes Q, O and (for award redemptions from QR's program only) X, U and Z if there is no immediate [(< 8 hours)] [scheduled] [direct] connection on the date of departure from origin, "

That means that the lowest ticketing classes are not entitled to free STPC but may be entitled to paid STPC. The minimum spend limits sound like an effort by QR to reduce the number of Free STPCs and is an addition to the existing rules rather than a replacement.