This is only the case if they can show that the crash occurred due to you driving at an excessive speed. It's by no means the case that getting into a crash on the autobahn going 200km/h automatically means that you're not getting a full payout.
Oh also, if you have vollkasko this is very unlikely to ever be an issue unless you were being grossly negligent (e.g. fiddling with the navigation while going 200km/h+), you're covered against "regular" contributory negligence.
