Seems that any fish could swim fast enough upwards to break the surface if it had a reason to...like if it was trying to escape from an unsuitable environment, perhaps.
I'm sorry but that is your opinion, speculation at best, and not a fact. The fact is that many fish are incapable of jumping out of a tank.
Let's take hippocampus reidi for example. The fish is incapable of breaking the surface fo the water with more then 10% or so of it's body (not a scientific measurement) unless it is suffereing from gas bubble disease or unable to regulate it's swim bladder in which case it can float to the top, but not jump out. Continuing with the same fish, given an unsuitable environment, such as being put under anesthetic with clove oil or being euthanized with Ms-222 the fish does not jump out of the water, when the conditions turn unfavorable IME.
I realize a reidi is not a clown, however not all fish can jump.

Many fish are notorious for being jumpers like some species of dartfish, pipefish, or gobies. Other fish are less likely to jump, but still capable.
Sorry but IMO the dog analogy is way to much of a stretch. Compared to many dogs natural roaming patterns in the wild, keeping then in a 3 bedroom house with a yard is pretty confining. That doesn't mean the dogs needs cannot be taken care of in a residential dwelling, or that the dog can not be happy there. Compared to the wild, where a small clown most often ends up as food, a 1g tank for a 1/2" fish, free of predators, with a prepared meal deliery service must be kind of nice.
No one is talking about keeping a 4" clown in a 1g tank the discussion is about a 1/2" clown, little different. Also different then a discussion about keeping a pair of clowns and an entire tanks stock of corals in a 1g tank that was setup on the same day. I'm sure Grunt is a very capable keeper, but even with his best efforts there is not many ways that scenario can play out. Sometimes the hardest parts of the hobby are the ones we can't plan for.
I'm not a clown expert, don't claim to be. If you have experience breeding fish, keeping a 1/2" fish in a gallon of water is not really that bad. Check out the tanks of clownfish breeders, open tops, hmmm. Check out there stocking densities too.
I'm not really trying to fight here, but acknowledge there are more ways then one to do things. Your condemming the succsessful experiences of others based on your opinions, rather then your experiences, it's a dangerous practice IMO.
"Great spirits have always encountered opposition from mediocre minds. The mediocre mind is incapable of understanding the man who refuses to bow blindly to conventional prejudices and chooses instead to express his opinions courageously and honestly. " Einstein.
