Source please. This is interesting.
What it amounts to is in Brawl the music was arranged in categories from A-Z in Brawl's coding. Two categories were absent in the list, the "O" and the "V" categories. If you look at the list below the "O" category falls in with new and miscellaneous series (L-S). Based upon this I have long speculated that there must have been a series (whether it be a stage or character) removed from the game.
A: Mario Series
B: DK Series
C: The Legend of Zelda Series
D: Metroid Series
E: Yoshi Series
F: Kirby Series
G: Star Fox Series
H: Pokemon Series
I: F-Zero Series
J: Fire Emblem Series
K: Earthbound Series
L: Pikmin Series
M: WarioWare Series
N: Animal Crossing Series
O: ????????
P: Kid Icarus
Q: NES Series
R: Misc. Series
S: Metal Gear Series
T: Super Smash Bros. Past Series 1
U: Sonic the Hedgehog Series
V: ??????????
W: Super Smash Bros. Melee Past Stages
X: Super Smash Bros. Brawl Series
Y: Super Smash Bros. Brawl Unknown Tracks
Z: Small Themes
I've also heard theories on why so many things were cut from Brawl.