Not used lastfm for about 2 years, but I doubt my listening habits have changed that much.
The unknown quantity will probably be untagged songs. Chances are they're rare soul tracks which will originate from the U.S.A..

http://xhochy.org/lastfm-nationstats...track.png-list

http://xhochy.org/lastfm-nationstats...e3859.png-list
http://xhochy.org/lastfm-nationstats...de3859.png-big
America FTW?

New Zealand is actually an archipelago.

http://xhochy.org/lastfm-nationstats...jdgun.png-list
Dang.

http://xhochy.org/lastfm-nationstats...ock83.png-list

^ My best guess regarding the unknown category is that they're all off that whole lotta official compilations I've got, in which case it'd be made up of a load of Jamaican ska and rocksteady, Latin American and African stuff or whatever.

Alice in Chains
The Allman Brothers
B-52's
Bad Brains
Bad Religion
The Beach Boys
Chuck Berry
Between the Buried and Me
Black Flag
The Breeders
The Byrds
Cake
The Cars
Chicago
The Chi-lites
Collective Soul
The Connells
Creedence Clearwater Revival
Fats Domino
D!ck Dale and The Del Tones
Willie Dixon
The Doors
Down
The Dwarves
Dysrhythmia
Duane Eddy
Everclear
Foo Fighters
Goo Goo Dolls
Guadalcanal Diary
The Grateful Dead
Bill Haley and His Comets
Jimi Hendrix
Johnny and the Hurricanes
Buddy Holly and the Crickets
Johnny Lee Hooker
The Hooters
Immortal Technique
Isis
Janis Joplin
Louis Jordan and His Tymapny Five
Kings of Leon
The Lemonheads
Lynyrd Skynyrd
Neurosis
Nirvana
NOFX
Mad Season
The Mars Volta
early Metallica
The Minutemen
The Misfits
Les Paul and Mary Ford
Missing Persons
Molly Hatchet
The Motels
of Montreal
Pantera
Pearl Jam
Pelican
The Platters
The Presidents of the United States of America
Elvis Presely
Pylon
The Ramones
Red Hot Chili Peppers
The Replacements
REM
Russian Circles
The Roots
The Screaming Trees
Slayer
Smashing Pumpkins
The Smithereens
Soundgarden
Stone Temple Pilots
The Stray Cats
The Strokes
Talking Heads
Television
Temple of the Dog
The Thermals
John Wayne and the Tennesse Two
The Waitresss
Ween
Weezer
Tom Waits
Van Halen (w/ David Lee Roth)
The Ventures
Gene Vincent and the Blue Caps
X
ZZ Top

I added some bands to your list. I didn't want to name bands just for the sake of listing them, but I don't know too much about 80's music so threw in B-52's, REM, Pylon, Guadalcanal Diary, they were from Athens Georgia which had a burgeoning music scene before Seatle stoled it from them.

http://xhochy.org/lastfm-nationstats...o1986.png-list

USA wins

Neat.

http://xhochy.org/lastfm-nationstats...ewife.png-list