This is a good point.  Their argument from parsimony seems to say - "we IDers don't have a huge number of physical laws (some unknown)  and coincidences of are events, we just have a single simple 'designer'".   However, for that concept to work, then there must be some relationship between said 'designer' and the actual universe, and a whole host of specifications of how it operats IN ADDITION TO the known physical law.   By postulating something over and above our known universe the IDers efectively double the knowledge we must have.  (Not only do we need to discover all physical relationships and entities, but all of them PLUS the 'design' entitis and their relationships with the physical).

I guess this is why Patton rejects simplicity as a criterion for a good explanation.