A b-side is more than just a song that sucked when they recorded it. More often than not, the song simply lacks the tone and feel of the album. Rather than meshing a bunch of friendly radio tracks and calling it an album, or as I like to call it, Pop music, good bands tend to create an opus of sorts. In my own experience with Pearl Jam, there are numerous songs that are just as good if not better (Yellow Ledbetter, Breath, Alone, Footsteps, etc) than the songs that made the album.