It's more likely that the BT and wifi don't have specific co-existence support, and BT is trampling over wifi or vice-versa. BT hops all over the 2.4GHz band, including all over the frequencies that wifi uses...

It is possible to implement coexistence, allowing either one to give way to the other depending on how important the data is, but there's little in the way of standards to determine how this is done (each chipset manufacturer seems to have their own idea), and unless the wifi and bluetooth are actually on the same bit of PCB then it's really unlikely to have been wired up. Given that a lot of PCs have wifi as a mini-PCI card and BT as a USB device, my guess is that this is what you're seeing.

eg:
http://www.wi-fiplanet.com/tutorials/article.php/1379911

Of course, if you're tightly integrating these things on a mobile device, you can do it right

Hugo