Offences under s 49(1)(f) of the Road Safety Act 1986 are absolute liability offences. The assertion of a claim of honest and reasonable mistake has no effect against such a charge: Skase v Holmes (Unreported, Supreme Court of Victoria, 11 October 1995, Vincent J).
In that case, Vincent J aligned drink-driving with the offences of speeding (Kearon v Grant (1990) 11 MVR 377), overloading a vehicle (Welsh v Donnelly  2 VR 173) and driving without valid car registration (Pilkington v Elliot (Unreported, Supreme Court of Victoria, 26 September 1991, Coldrey J) . The absence of a requirement on the prosecution to prove any intent to a charge of exceeding the prescribed concentration of alcohol has become the accepted law in Victoria. That’s been the case for so long, it’s difficult to imagine any other legal position being adopted.
You might think a system which allows Proudman v Dayman as a defence would make the enforcement of .05 legislation unworkable. Many drink-drivers would not intend to place themselves over the limit, particularly since alcohol influences judgment. However, many jurisdictions allow a claim of honest and reasonable mistake, and their road tolls, etc. aren’t very different to ours.
In NSW, drink-driving is an offence of strict liability. Defences of honest and reasonable mistake are available, and sometimes successful. In DPP v Bone  NSWSC 1239, the accused was found not guilty of drink-driving charges after convincing a magistrate that his beer had been spiked with vodka without his knowledge. The DPP appealed but the magistrate was found to have been justified in his decision.
In Mendolicchiu  NSWDC 182, the District Court considered an accused’s claim that he had inadvertently consumed a cough mixture containing alcohol, and that this combined with other alcohol had led to a reading in excess of the prescribed limit. The District Court applied the precedent in Bone, as well as a line of Tasmanian authority, and quashed the conviction.
I emphasise that such defences would not succeed if argued in Victoria. But our law could easily have gone the other way.