I heard the strangest thing in a GAF impressions thread about the Daigasso! Band Brothers DX downloadable demo that just came out: apparently, you're only allowed to download 100 out of the 200 available extra songs—and once downloaded, you can't delete or replace the songs.

I confirmed this as best I could with an automatic translator at Nintendo's BanBro DX site, which says (slightly edited for clarity):

In addition, after you download 100 [songs], can you download more?

When 100 songs are downloaded, it is not possible to download it any more. It is not possible to overwrite due to rights restrictions on the music preventing the deletion of the downloaded music or replacement. Please use the audition feature before you download.

The "audition feature" mentioned above is part of a new feature recently highlighted on the game site. There are two "radio stations" in the game; one plays songs you have on the card, while another will play songs from the downloadable content. If you hear a song you like on this latter station, you can elect to download one.

100 songs, in addition to the songs that come with the game itself, is far more than just about any other regularly-priced music game has on offer. I can't help feeling that I'd happily drop a few bucks to unlock the rest, though.