Something that just occurred to me. The point of view of the splash screens is not looking down through the ice. It's looking up through it, from below. There are stars visible through the opening, after all. Also, it's lighter in the center, where the ice is broken, as though there were light coming in from the other side. If we were above the ice, the whole expanse would be light, and it would be darker near the center, since that's where the dark hole is.
This might just be a bit of artistic license, to make a cool star-speckled background, or it might be a literal, intentional direction. Most people seem to be thinking we're going to see something under the ice, when it's all cracked away and we can see through it. But that's not the direction of the images. They're looking up and through it, as if we were the ones buried under the ice and are now breaking through. So are we in Diablo's POV, as he breaks out of his frozen hell?
Are we going to see what's breaking through the ice, or are we the one breaking out, and we'll see what's on top of the ice in the 6th image?
The Frozen Throne was the receptacle of the soul of the Elder Shaman Ner'zhul following his transformation into the dreaded Lich King. It was shattered by Arthas Menethil, and the remnants now serve as the actual physical throne of the new Lich King created from the fusion of the souls of Arthas and Ner'zhul...
The ice fades to black as you work your way from the middle. (If we were on the outside looking at a bock of ice, or a wall of ice, wouldn't the ice be shaded differently?) When you consider that, yeah, it does look like we're the ones trapped inside a tomb of ice.
Wow, I assumed that was what was happening right away when I first saw it. I never even thought that we were looking INTO the ice from up top because of the lighting, I just thought that when people wrote under the ice they were thinking of something completely different...
I guess that means I'm smarter than all of you combined.