These bonus tracks are meant to increase sales in certain countries. In Japan and many parts of Asia, for example, the bootlegging industry was SO huge that most consumers would buy a cheap bootleg of a hit album, rather than the real thing. One bootlegger would buy the album, make hundreds of copies, sell them at little shops and reap the profits - while the artist and studio label made nothing.
Hence to spur sales for the real album, not the fake one, extra songs would be included. Extra songs were also added due to the high costs of CD's in many markets. Fans would rebel at paying so much for a CD with only 11 or 12 songs - but add an extra song or two and now it's at least worthwhile buying the real thing.
Even though CD sales in the U.S. have plummetted, so far, labels and bands have felt no need to add in extra tracks, unless it was a "special edition". Note that in the U.S., more and more special edition CDs and DVDs are being released. Often there's the normal version - but if you really like an album (or the artist) or a movie (or actor/director in the movie), you can buy the special edition at a higher price with more "goodies". This is how the U.S. entices sales.