I was wondering the same thing. I don't think the low iron glass would make a difference though, my frag tank is acrylic and it the same thing, better from the top.
Great discussion, I have no clue. I was selling some clams once and I had a guy come over and check them out and accuse me of doctoring the pic's because they didn't look like the clams did in person. I couldn't convince him to look top down and prove the pic's were accurate.
I agree with FishLipz. There are many things in nature that seem to glow brighter or have more vibrant color when the light hits at certain angles... I'm guessing the light hitting straight on has something to do with it