Forgive me Peter, I've been playing catch up for the last week on the thread so I did look to see if this was addressed, but I apologize if it was and I missed it. This is definitely not the case with fish that are likely to jump. It has nothing to do with whether or not they are happy, fish like wrasses, basslets, pseudochromis, and anthias (among others) are some of the worst jumpers. They don't jump because they are unhappy and want to escape the tank, they just jump when something startles them either inside or outside the tank.
It's kind of like if you were watching the tank and someone snuck up behind you and poked you in the side. You'd get startled and jump a little. It doesn't mean you're unhappy, it's just instinct. Same thing with fish and when something startles them they can dart in any direction, including up and sometimes this means out of the water. The fish have no concept that they can dash up and out of the water and somehow not come back down. Obviously in the wild fish are usually facing unlimited space to dart in all directions including up and if they do leave the water their is nothing stopping them from falling back down like there might be on our tanks at home.
This leads many people to cover their tanks with things like eggcrate (not the best idea as it acts as a light diffuser). A better idea is to use very fine netting because this has less impact on the light and no impact on evaporation. You can also feed through it so no need to move it all the time. There are online vendors like Bulk Reef Supply that even sell the netting by the foot and with plastic frames so you can build your own covers that can then easily be moved for when you need access to the tank.
I will give you that it's not like a fish is destined to jump out, but it can, and very often does happen. Though the more room the fish has to dart around like there is in your tank, the less likely they'll end up outside the tank, it's still better to be safe than sorry.
Just wanted to throw in my .02. Hope you don't mind the perspective (though considering your posts, I doubt you will).
it shut down the water supply to half of Guelph. 
Just kidding buddy, you have an infinite amount of knowledge and wisdom to share with this community and Peter is very lucky to have someone of your caliber working alongside him in this build. Now all I need to do is have you commission my next tank build! Will you work for Corona's?
