Miracles

I am listening to an interesting lecture series on the Life and Teachings of Jesus, by Dr. Daniel Doriani from Covenant Theological Seminary, and in one of the lectures he asks the question "Do miracles take place today?" I thought it was an interesting question. Dr. Doriani's answer was no, at least not in the biblical sense. He defines biblical miracles as "a direct, unmediated act of God in the external world in which He works outside the common course of events to reveal Himself, to authenticate His servants, and to manifest His nature and redemptive purposes" and he says that using this definition, miracles no longer occur today. I think this is interesting to think about. Is this an appropriate definition of miracles? Is there some form of miracle that is not included under this definition? Doriani makes sure to distinguish between acts of God and miracles. Birth and "miraculous" healings from disease are acts of God. The biblical forms of miracles are used by individuals (miracle-workers) to establish the fact that they are agents of God. Since God no longer has any agents in Earth in the biblical sense (i.e., prophets, His Son, etc.) then he no longer peroforms miracles. Is this just semantics, or is there a substantive difference? Thoughts?