If I recall correctly, Genuis uses play info from users who have Genius enabled. It will look at what other songs appear in the same playlist, what songs users choose to play next and so forth.
Downside, is for unpopular songs. If Genius can't see enough users with that Fleetwood Mac song then it can't make recommendations.
Test: Get all Axiom Forum users to get a copy of that song and make a playlist with it and update Genius. See if your side works any better!
*All the above is my recollection and should be taken with a grain of salt.
M22, VP150, QS8 <--all v2
Sub: Outlaw LFM1-Plus
Denon AVR1910, Panasonic Plasma 50" S2