Here is an excerpt from the RCI website about their air arrangements:
"...once tickets have been issued it is the airlines responsibility to protect schedule changes resulting in misconnecting flights."
That pretty much sums it up for me. Now granted, RCI knows what flight you are supposed to be on and if at all possible they will delay departure of the ship within reason. But they cannot wait indefintely for you if your flight is delayed. My understanding (may be wrong) is that, for example, if you made it to Miami but the ship has already sailed then you are now going to have to pay to catch up to the ship. RCI will help arrange it but they have no obligation to pay for the extra airfares.