Remember that GM scrambled to cash in on the SUV bandwagon (consider the profit margin
) as fast as they could. So many of the SUVs were hastily derived using current pickup truck platforms.
Th P/Us had the least amount of leading edge technology built into them, thus some holdovers such as drum brakes persist. Eventually, they will update the rest of the systems, but I would agree that the third generation Escalade should be sporting 4-wheel discs by now...