From the comments to my post on the role of a pastor, I think maybe it would be profitable to outline what I see as what a Quaker pastor does in an ideal setting, and then maybe some healthy critiques.
Why do some Quakers have pastors? I think because we find that some people are gifted and called in a way that they really should be paid to do the ministry they are called to, because in order to do it effectively they need to be financially released to do it full time. Although we're all ministers, some are called to minister by working in a grocery store, an office, a school, etc. But some are called to bear the title "pastor," and do the work of "pastoring," which, as Friend Marshall commented, has to do with shepherding. This can be shepherding those in the "herd" already, or I suppose finding other "sheep" to join the fold. This shepherding can include doing administrative tasks, providing leadership in creating a welcoming environment where all can feel comfortable and challenged in worship, visiting people, helping others lead small groups or classes, providing counseling services, and many other tasks.
Many of these things could be done by other people in the meeting, but the thing is, they don't always (or even often) happen unless someone is assigned to them, and even then a lot of times volunteers don't have time to do what they say they will. So perhaps it's out of expediency that some Quakers choose to hire ministers--it's easier to pay someone to do it than to do it ourselves.
But I think it's also a sense of leading and calling. Not everyone is skilled in pastoral areas, and some people are. (Just like I would be incredibly bad at any job that required a great deal of techinical or mechanical savvy!) So it makes sense to hire someone who is gifted in those areas, and who enjoys doing the work and feels called to it.
Pastors often do a lot of research on things that other people don't have time or interest in learning, but that are of significance when developing and teaching good theology. Theology can be helpful or harmful in creating a worldview and in shaping one's view of who God is, and so I think it's important to have people who have thought well about all angles and have listened to other voices through being taught by others and through reading what others have to say. In this way, even if everyone in the meeting doesn't do all this education, they beneift from it by a pastor who hopefully teaches it effectively and models it by living it out in helpful ways.
One doesn't have to be trained at "Oxford or Cambridge" (or even Princeton...) in order to be a minister and to share and live as God asks them to, but I think it's good for some people to have some sort of training, or else good theology goes out the window, and people learn very harmful theology instead.
I have to respectfully disagree with Friend Marshall that pastoring is not from a sense of calling, but is mainly based on one's skill set. In our Yearly Meeting, anyway, we expect pastors to be called to that ministry. We even call it a "call" when a congregation invites a pastor to work for their meeting. The congregation senses that God is calling that person to ministry there, and they invite them to do so, and release them to do so by paying them a salary. I do agree with Marshall that this call could end at any time, and hopefully the congregation and the pastor would discern that together.
The question is, is a pastor the one teaching and equipping others to serve the larger community? Is the pastor discipleship-focused, focused inwardly on the congregation already present? Or is the pastor a model of how everyone should interact with the community?
I think currently in our yearly meeting, most pastors are by necessity discipleship-focused. This happens for several reasons. 1) There is so much biblical and spiritual illiteracy today that many who are long-time Christians know nothing about the faith they profess, so the pastor spends a lot of time doing basic education that used to happen in the home or in First-day school. 2) Congregations pay a pastor so they (at least subconsciously) think the pastor should meet and cater to all their needs and expectations. 3) Our society is so individualistic that we forget to care for one another, so if the pastor doesn't do it no one will!
The next question is, is this how it should be? Perhaps some people are more gifted at discipleship, and others have more energy around going out into the community and serving there. But shouldn't we release people for ministry who are doing some good for the world, not just for ourselves?