If you ever attended an LDS meeting you would perhaps understand better. For one thing there is no "preacher" per se. There is a Bishop with his two counselors who preside over the meeting but do not necessarily preach at each one. The members will be asked to prepare a talk to give. There are usually two youth speakers and two adult speakers along with singing of hymns. All without monetary payment. As dbackers has mentioned there are no paid clergy within the church. It is all lay clergy, they all have jobs and other sources of income that are separate from their jobs in the church.
Paying tithing is a privilege. Tithing funds are always used for the Lord's purposes-to build and maintain temples and meetinghouses, to sustain missionary work, to educate Church members, and to carry on the work of the Lord throughout the world.