To be culturally relevant means (to me) to effectively communicate to those you want to reach. The style of worship and music is most often what is discussed, but it can and should involve also the way we teach, preach, disciple and evangelize, etc.
Churches with more traditional music can be relevant if they have a passion to reach people where they are. More contemporary churches have decided they want to reach a more contemporary-minded population. Music style will always draw those who have a taste for it!!
If a church is teaching biblical doctrine, a clear gospel and making followers of Jesus Christ- let God's work be done! Praise God, we can all do a work in our own way as we are led by God.