Culture-relativity

Same in France, with the difference that "docteur" refers to a medical doctor 99.99% of the time. Other docteurs never use their title outside work (and not much even there) so the "medical" adjective is not needed and never used. To resolve the 0.01% ambiguity, French has instead a... shorter, single word for Medical Doctor: "médecin"!? Go figure.

In Germany, not all practicing physicians actually have medical doctorates (it's not required; what is required to be allowed to see patients is an official government-controlled exam). In everyday usage, however, even the non-doctors are still often addressed by their patients as “Herr Doktor” or “Frau Doktor” as a courtesy, simply because the notion that “physician = doctorate” is pretty deeply ingrained in the population.

Incidentally somebody mentioned that in the UK, physicians go by “Doctor XYZ” except that when they qualify as surgeons they revert to “Mr. /Mrs./… XYZ”. This is because way back when, medicine and surgery were completely different disciplines. Actual physicians weren't keen on the bloody business of surgery, while surgery, especially wartime surgery, was usually undertaken by barbers (presumably because they had sharp knives to hand). Physicians, who in spite of the limited scope of pre-scientific medicine were usually university-trained professionals, used to look down on surgeons, who were mere tradesmen – glorified barbers – who had gone through an apprenticeship.