I think you're confusing it with the first Castlevania, which was originally on the FDS (though it was eventually released in cart format for the Famicom in 1993). I actually just bought a Akumajou Densetsu (CV3) Famicom cart, I'm waiting for it to come in the mail (see the last link in my post above). Can't wait for it to get here, the music is so badass in that version!
I almost bought a FDS, now that I have a Famicom, and I would definitely pick up Akumajou Dracula for it. I read that there's some graphical differences in it, and that some music is different too. However, I played through the FDS version on an emulator and didn't notice anything from the NES version (which I've played a kazillion times). I would probably pick up a FDS just for a collector's sake, if it weren't for all the horrible things I've read about reliability problems.
I love the differences imports can have, and I'm a nut about that kind of stuff. I'll compulsively buy a different version of a game if I find out I'm missing out on stuff. I bought the SFC version of CV4 because of the censored stuff, and the Saturn version of SotN because of the extra areas. I consult this link all the time:
http://castlevaniadungeon.net/games.html
If you click on a game, you can click on "foreign" which usually lists the differences between regions. Pretty neat.
