Aquarium designs contradict my understanding. Am I wrong?

I've seen these aquariums with glass covers over the tops. Doesn't this contradict some of the principles?



I thought that enclosing the top would trap nitrogen gases that are being released from the surface agitation and would be counterproductive. Wouldn't this also contribute to less dissolved oxygen in the aquarium? Another thought would be that it would collect salt deposits and reintroduce clump of salt to the water which potentially could burn the corals tissue if contact was made. Then there is the idea that glass will lower the light penetration of the water and obstruct it from reaching the corals as effectively.



Am I wrong here?