I blame the original Ravenloft module, and Ireena/Tatyana. That's not the actual reason, but I like to tie it to that, regardless.
As far as I know, that came about due to an early 70s TV version, made by the same person who made Dark Shadows and starring Jack Palance. IIRC, that was a plot point for Barnabas in Dark Shadows, and he reused it in the Dracula movie.