In a nutshell, the wifi and bluetooth chips can't be quite so compatible. The basic difference between the two technologies is that Bluetooth can work inside of any device, and has a limit of 8 devices that can communicate at once. To the contrary, wifi requires a processing chip in at least one of the devices communicating, and many more devices can be wirelessly connected depending on how you have things set up.
Bluetooth is also more power efficient so the batteries last longer on portable devices. Wifi has faster and usually furter connection distances.
Each technology- bluetooth and wifi- is optimized for certain purposes. While there's definitely overlap in what you can do, you'll accomplish some things better with one technology versus the other.
Blue Essentials has some great guides on Bluetooth technology:
http://www.blueessentials.com/info.php
IOGEAR also has an exceptional wifi guide in pdf format:
http://www.iogear.com/guide/WHY%20WI...(lo%20res).pdf
Hope that info helps!