Expository Only?

My favorite section from Give Praise to God this week was "Expository Preaching as Worship." (109)  I appreciate the book's fervor for expository preaching in today's churches, because many are lacking in anything but spiritual milk.  Expository preaching is important, and when done correctly, it encourages growth to a higher degree than other forms of preaching.  However, is it the only way?  My church, while it usually uses expository, will sometimes have a special emphasis on a sunday and speak on a topic rather than a passage.  I even think of the speaker we had in MPS yesterday who said that, as a worship pastor, he preached about worship and music.  That is not going to be taking a part of scripture passage by passage.  My question would be, can we implement other forms of preaching than expository only?