There are 2 kinds of audio-bluetooth profiles (3 actually). Two of them are for headsets/handsfree kits, and only transfer mono audio on a pretty crappy quality, pretty much the same quality as your cellphone will give you, certainly not suitable for a movie, though perfect for VoIP phone calls like AlanW mentioned. Then there is a true "Bluetooth Audio" profile, this supports real stereo audio in high quality, like these ones:

http://www.expansys-usa.com/product.asp?code=114076

Because so few laptops come with the right bluetooth profiles (for Bluetooth Audio) they include an audio-in to Bluetooth adapter.