GKV nope, just a pilot!
DP Davies writes in Handling the Big Jets (or the Bible)that the indicated stall speed increases for two reasons.
1. Due to compessibility effects causing a larger difference between EAS and IAS. That I can cope with. But...
2. "The actual EAS stall speed increases due to Mach No. effect on the wing. At very high altitude the EAS stall speed occurs at a significant Mach No.(180 knots = 0.61 Mach No., for example); the pressure pattern is disturbed and a higher stall speed results"
Could someone explain, in easy words writ large for pilots, the second one please? Ta.
Also, was my opening assumption incorrect; nobody actually said for sure.