It's more a question of the manufacturers of these dongles not
considering Linux in general ( as usual !! ). The Linux community is
therefore left to 'pick up the pieces' and figure out how to get these
dongles working :-( This takes time unfortunately but there are some
makes that have been verified - check the list here which gives the
status of development for drivers plus the devices supported.

http://linuxwireless.org/en/users/Devices/USB