CamelFilters, you don't get it: all those V-8s get horrible fuel economy. The GS 450h, on the other hand, has a V-6 paired with HSD and it will get mileage probably around 24-26 mpg real-world, while going 0-60 in 5.2 seconds, and being very reliable and luxurious.

The cars you mentioned are far less reliable (especially Mercedes), far less fuel-efficient, and in some cases are less luxurious and slower to boot. The Audi A6 4.2L goes 0-60 in 6.7 seconds according to a quick Google search.