That is definitely not the case. With many subjects, just flashing an image on powerpoint does not do a good job expressing the logical progression of the concepts. A good example of this is any high level mathematics. It is *much* easier to follow a clear derivation as it is written with a narration by the professor, than it is to follow a written version in powerpoint, even with the widgets powerpoint has.
If the students could understand the subject just by reading a powerpoint, then there's no reason to have the professor there in the first place. Just email them the powerpoint and tell them to stay at home.