All S500s are long wheel base standard. S600 and S500 all come long wheel base standard S430, S350 have the option of shorter or longer wheelbase (atleast in the w220 and w221 models). The pics remind of the ML benz not G class I dont think the G class's shape will be changed so much so that is resembles the ML as its a classic shape. This is a new class by itself introduced by Mercedes its the GL class starting from 07 while the G class is still going strong. The GLs direct competitors are listed below.
Audi Q7
Cadillac Escalade
Lincoln Navigator
Porsche Cayenne
Range Rover