While I can't think of a whole lot of reasons, especially without I-MAG, you may want to check out this site:
http://god-media.blogspot.com/
http://god-media.blogspot.com/2006/06/imag-what-i-like-and-what-i-dont.html
The author has some pretty good comments on the use of visual technology in his archives (have to do a little digging) and some pointers to other websites.
To me, different images on each screen would be very distracting. I'd be more focused on what was going to change next rather than my focus on worship. I could potentially see it for videos that have some form of dialogue going on between multiple people, but other than that I think you'd have a lot of people becoming unfocused as their attention would be called from one screen to the other. It would also be hard on some people who are sitting in a bad position to see one of the other screens.
In Him,
-Peter Schott