Surely you guys have heard that the "DLC" characters in Street Fighter X Tekken were already on the disc, right? and within weeks of the game's release, people have already hacked the disc and started using the characters in online matches? (Certainly pissed Capcom off, but IMO it's their own fucking fault) ... Trust me I'm going somewhere with this.
Hearing that story reminded me of a similar incident that came about after the release of one of the PS2 DDRs, it the jump for the rest of the story behind this elusive unlock!
If history has shown us anything, it's that if companies decide to hide something on the disc/cartridge away from gamers, one way or another they'll find some way to access it. Back when DDR EXTREME was released on the US Playstation 2, savvy gamers who were able to hack the disc discovered that there was one song in the game that no one could figure out how to unlock it.
Playing 1000 songs didn't seem to do it, even completing the game's 'Mission Mode' didn't do it if 'memories' serves... it wasn't until a Burger King promotion for DDR came around that the button code to unlock the song was revealed.
Up until that point the easiest way to play the song was to download a save file with the 'edit' data for the steps onto your memory card and play the song in edit mode.
Oh and for those interested: at the title screen on controller 2 input Right, Right, Right, Right, Up, Up, Up, Square, Left, Left, Down, Down, Down, Square, Square, Select. the *NEW!* icon should appear next to the 'Information' option and Memories will be unlocked for play in all modes!