First of all, what is tithing?
It is giving up material goods, sometimes money, to "the church". Now, some do it for their own reasons, and some do it for the glory of God. Where those two reasons diverge, is the manifestation of the intent of the person in subsequent words and actions. Only God knows the hearts and minds of humankind, and he'll know who is doing it for Him, and those who are doing it for themselves.
Secondly, what is "the church"?
Now, if we assume that the bible is talking about a physical church, a building or structure where a congregation gathers, we are wrong! The church the bible is speaking of, are the people themselves. Wherever God's people are, there is His "church".
Therefore, tithing to the church, is giving to people in order to glorify God. When we do this, we are given bountiful blessings to continue in ministry to others. We plant the seeds and give a little water, but God's glory is what makes it grow.
When viewed in this context, Jesus' teaching that we should give without seeking anything in return, makes complete sense. Of course, the shepherd is worthy of his hire, and so this is why we are blessed by God when we DO what He asks us to do!