The online version of Christian History has an interesting article about the "altar call." I was raised in churches in which the public invitation was the main aspect of each service. In fact, the number of those who "walked the aisle" became an indicator of God's blessing. I don't deny that many people have come to Christ through this method - I am one of them. However, amongst many evangelicals and most fundamentalists in particular, it is a sign of orthodoxy.
As is true with everything, there is a theology behind the practice. Sadly, many are not aware of the theological implications, or, due to the wholesale capitulation to the spirit of pragmatism, do not care. 1 Cor. 1:21 tells us that it is the preaching of the Cross that God has chosen to use to save them that believe. Perhaps the reliance on the "new methods" indicates a failure to adequately and powerfully preach the Cross.