Actually, once you take into account that Whedon's Dracula isn't, and doesn't in any way pretend to be, Stoker's Dracula, it might make more sense that the two characters are so different. Stoker's Dracula was based on Vlad Tepes, a real historical figure who, as well as I can recall (and it's been several decades since I read a condensed version of the book, so someone please correct me if I'm wrong) didn't become a vampire by the traditional method of being turned by another vampire. He never displayed any sort of "game face," remaining totally human, always. Also, there was no siring necessary with his victims. If they died from his bite, they always came back as vampires. His powers were unique because he was unique.
Whedon's Dracula was based on what must have been dozens of interpretations of the character, so changed over the years that they bore little or no resemblance to the "real" Dracula. It would be like trying to portray Tarzan by studying the movies of Johnny Weissmuller, Glenn Morris, Gordon Scott, and the other actors who have portrayed Burroughs' Lord of the Jungle, without ever going back to the source. Whedon tried to fit a character into the Buffyverse who never had any real business there in the first place. He tried to do it by simply saying that everything unique about Dracula was the result of Gypsy magic, because without all those unique things, the character just wouldn't be the Dracula we are all more or less familiar with.
Whedon's Dracula isn't the character Bram Stoker wrote about, he isn't Bela Lugosi, and he isn't Christopher Lee. He's bits and pieces of all of those, with a little Whedonverse magic tossed in for spice. He's a completely different character, and I think that the actor who portrayed him that way did a good job of NOT trying to be Lugosi or Lee, whether that was his intent or the director's.