I ran into this the other day and didn't think much more about it. Yesterday, I heard an article on NPR about it. While the image that accompanies the song is obviously anime (I missed where it was from--if you know, tell me), the band is Loituma, a Finnish folk music quartet. The NPR article said that some Finnish folk music was intended to be easily improvised, so a single song could be performed for hours on end, creating a trancelike effect in the players (and the listeners).
Finnish isn't supposed to be closely related to other languages...I wonder if the same barbarian tribes that ended up in Japan split down the middle and travelled to Finland, too.
Now, we just need the same thing for Kate Bush's Army Dreamers.