I don't know if it's common practise in other countries. In Sweden where I work it is. I think the rationale is the following:
It's a lot faster to use a voice recorder.
A doctor's time is worth a lot more than a secretary's (in the sense of pay and rarity)
Using a voice recorder lets us review lab results, radiology etc at the same time as recording, not having to switch between tasks.
-Doctorss wont have to be good spellers or think about building well thought out sentences. We also dont have to look up classification codes for procedures and diagnoses. All this will be done by the secretary.
Of course we have to review the teanscribed result. At my hospital, all doctors carry smart cards and use the personal stoed private key to digitally sign every transcribed medical record entry.