I'm in the top-down crowd as well. Let's face it, a lot of corals (most of them) look like crap from the side. I like to take top down pics and use them as desktop wallpapers to remind myself why I go through all the trouble of trying to keep SPS in the first place
Sure, you don't get to see your corals top down every single day, but that's why you take top down pics ! So you can sit down at your desk or your phone or tablet and view them whenever you want.
As for the vendors perspective, their number two priority is to sell stuff (number one would be to keep stuff healthy and alive). They are really no different than any other industry that sells stuff based on how stuff looks. They need their stuff to look as awesome as it possibly can, and that means top downs. Open up catalogue or a magazine. All of those swimsuits sure look good, but in actual practice most of them are crap. They're just photographed very well :-)