The high-rel chips are tested at all three temps. Commercial
often enough does not test more than one temp with the rest
handled by correlation. Hermetic packages cost 100X or more,
what a stamped leadframe and a squirt of molding plastic
do. The list goes on; every element of the part is specified
to be "best" and somebody has to foot the bill.
Hi-rel parts also have a whole raft of high manual effort
"Group" testing and per-unit inspections that add to cost.
Then you have the limited sources of supply, which lets the
manufactures who -are- willing to play, price a lot higher
than in a wide-open, high volume, cost-competitive market.
All of this has not a thing to do with whether the circuit
itself is high temp capable (150C is not high, it's only just
toasty warm).