That update doesn't increase the speed of the drive, it allows the drive to work woth DVD-Rs aimed for 4x recording. Right now the superdrive is designed to work with 2x DVD-R media, but as stated, any Mac with a super drive built after a certain date, I think November 2002 are already updated.
well as jb said, it's not the speed that's changing, it's the format that can be handled, or thereabouts. in my younger days, I would've projected as to how it may be possible for software to make up where hardware leaves off, but for now I'll just let it go. If anyone cares join in, great. If not, Q.E.D.