According to the statement, Nintendo has received complaints from Smash Bros. Brawl buyers of the Wii being unable to read their newly bought disc, or of videos chopping up during playback. These users claim to have had no such problems with past games.
Nintendo has come to the conclusion that the problem has to do with dust and tobacco building up on Wii laser units. This effects Smash Bros. Brawl while leaving other titles unaffected because the new fighter uses a dual layer DVD, which is apparently more sensitive to a dirty lens.