<Correlation> To illustrate: Is a crash at 80 going to be autmatically more damaging? By your logic,yes, but in fact not so. Roads where the NSL applies are often dual or motorways, so the rate of closure may be significantly less than in a head on in a 30 limit.
The stats show that speed alone accounts for less than 10% of all accidents, and that is not necassarily illegal speed. Not the 1/3 of all crashes or whatever the Speed Kills mob like to suggest.
Bad driving includes speed, sure, but rarely just that.