At the flight sim conference back in munich Mr. Randazzo had mentioned they actually had to remove a significant amount of dust and dirt on the pictures they made of the real airceaft via Photoshop or something. The plane was really that filthy

The thing is, it's one thing to keep your privately owned aircraft clean.

But when you have everybody using one jet at any given time, on a tight schedule, it's kinda tough to keep it ultimately clean in between flights. Unless you're these guys ;

Believe me it doesn't take long for the cockpits to get really dirty. NGX is very realistic except for the displays. I don't know any pilots who would not clean screens that were that dirty but there are probably some out there.