I have to agree with you on that one, there is a defference when it comes to nerd and otaku.
in my mind nerd is someone that knows a lot about a number of things (ie. Computers, technology, video games, codes, and other thing along those lines)
Otaku on the other hand only takes joy in reading, drawing, watching, writing, and listening to anything that has to do with anime, and nothing else.
I am a nerd, with a little otaku mixed in, but I don't spend all my time with anime, but I do, when i have the time like to draw, and watch anime.
I am also very picky about the kinds of anime I watch, where Otaku's are not.
I hope this has help to clear some of the misunderstanding that people have when it comes to nerd vs otaku.