Should We Have Worship Leaders?

In his book Worship Matters, Bob Kauflin argues that we should have worship leaders.   I've been reading his book off and on during the past month or so.  The first few chapters were thought-provoking and helpful in terms of what worship is and our attitude as we approach worship--specifically on Sundays, since giving God glory (worship) takes place outside of the church assembled.  But as he turns to the concept of worship leaders, I find his argument a little shaky.
From chapter 6, "What Does a Worship Leader Do?":

We can glean some important principles from Old Testament Levites....But we can't transfer everything they did then to what we do now.

A few paragraphs later:

Second, the most important worship leader is Jesus. He reveals God to us and through his perfect sacrifice provided the only way into the Father's presence (1 Timothy 2:5; Hebrews 10:19-22). 

We can't do what only Jesus does.

And a little further on:

Humanly speaking, the pastor is the worship leader.  He is the one responsible before God for the corporate worship of the church (Hebrews 13:17; 1 Thessalonians 5:12-13).

In light of these reasons, which are obviously not exhaustive, is there a biblically based role for a non-pastoral worship leader?  Kauflin seems to think so.  His argument appears to go something like, "There's not a lot of biblical precedent, but since we do this, here's how why should do it."  But on what basis?

It's hard to see how the role of "worship leader" flows out of biblical principles.  Especially when "worship leader" means the stereotypical guy (or girl) whose primary qualification is ability to play the guitar, rather than pastoral qualities or theological training.  Should such a person lead in a central aspect of the gathered church's Sunday activities?

Perhaps the problem is that the role of worship leader, like the function of Sunday School, is practiced from habit rather than biblical principle, and in the absence of biblical principles, almost anything goes.  We need to take a long, careful look at how we do worship, specifically the musical aspects, and who we designate to lead in those activities.