Yes, that's right. It is absolutely legal to drink and drive. It's only illegal to drive while intoxicated or impaired. Even though both these terms are subjective, the legal system is inflexible and relies on questionable "science" to convict drivers of being drunk.
Many arrested drivers admit they were drinking before driving but disagree that they were drunk or even impaired. Having no experience with the criminal justice system and faced with the pseudo-science of field sobriety tests and the Datamaster machine results, people are encouraged to lie in court in order to accept a "reduced" sentence. Many attorneys tell their clients that they must admit that they felt impaired because the alternative risk at trial is the "more serious" offense of Operating While Intoxicated and the temporary loss of their license. Unfortunately, for the most part, these attorneys have never taken a drunk driving charge to trial during their careers.