This is a never ending battle. I've noticed that the best response is I can re-draw it, it's $75 an hour with a 3 hour minimum.
Thats when they magical get the file or they tell me to re-draw it.
After I re-draw it, I create .eps, .pdf, .png versions in color, and black and white. I than create a little notepad file explaining what each file is and what it's used for. I take all of that, thow it in a folder, zip it and e-mail to them. This way they will always have that logo in a vector and raster formats in a easily accessible place.