The purpose of EGR is to reduce peak combustion temperatures, which it does by injecting inert gas into the inlet charge, reducing the amount of oxygen present. Exhaust gas counts as inert becuase all the oxygen should be used up. Of course it's hot and full of soot, but it is inert!
The Environmental reason for EGR and peak combustion temperature reduction is the reduction of NOx emissions. NOx - oxides of nitrogen - are formed by the nitrogen in air in the inlet charge being burned, oxidised by the high temperatures that can be reached in a modern engine. Peak comustion temperatures occur at peak load situations and are transient - accelerating away from traffic lights, opening up at mid-speeds and the like. EGR controls these transients by reducing the oxygen content, resulting in unburned fuel coming out as soot. Way to go for the environment, guys.
Now, if Renaults are failing becase their EGR is sticking shut, I would guess that they are boosted more than the VAG engines and make much more use of EGR to control combustion temperature.