Maybe the problem with the Sirocco is that it represents a real life car you can buy. I imagine that VW are quite picky when it come to the dynamics of the car. In these litigious times, no car company would want to be held over a model that does not conform to the actual car. I can just see some half-wit wrapping their nice shiny new car around a lamp post and blaming it on a poor simulation that managed to take the corner.
Maybe I'm way off mark, but it would make sense.