I'm looking for the same thing. Softinterface has a product called DocDiff
that does only the outline items in a presentation. Which is good if you
don't want to compare graphs, tables or imbedded objects.
I haven't heard of any programs that can do this. Unfortunately for you,
that's not too surprising, considering the amount of work it'd take to write it
vs. the relatively small demand there is for such an animal (we get maybe one
or two posts a year here asking about this).
If you need to flag differences for later analysis, here's one possible
approach: Export all slides in the presentation to relatively high resolution
bitmap files then use an application that can do image manipulation to subtract
the data from one image from the other. That will give all zero data or a
totally black image if the two slides are the same. Any non-zero pixels
represent a difference between the slides that a human could investigate.