It was more the safety factor. Having piles of rocks in it (being for the Malawis) we figured it wouldn't matter if they accidentally toppled onto ply but could crack glass. Less chance of stress fractures in an earthquake too. This tank will be set up in our computer room and there are usually 8 or 9 computers, printers, scanners ect sitting on the floor around the tank. If it leaked we would lose a lot of stuff.
Also easier to drill holes in