Also, the freeboard on most bigger cats, makes leaving a dinghy up there very difficult, since you'd need davits or something to haul it out of the water. You wouldn't want to drag a dinghy over the decks and scrape the hell out of the decks.
I just hate to see all that space wasted up there while cluttering up the back of the boat. A Zodiac doesn't weigh much, how about if I separated out the motor and only stored the inflatable on the forward deck?
I was kind of hoping it might even be possible to carry two small inflatables under the trampolines of a larger boat. I guess that's out of the question too...