5) I haven't seen much steel decoration in recently made levels. Mostly it was used in the original L1 and in some early Lemmix levels. So I have to ask: Why do we want to decorate steel, when there is so much else one can decorate?
Cart before horse, I think. The reason Lix levels don't decorate steel is that the game engine doesn't provide the option of doing so, without the decoration becoming a non-steel area, which allows the player to cut into the steel and is almost always undesirable from the designer's point of view. So we end up with levels that look gorgeous in other respects, but the steel is, out of necessity, barren and clinical.
Mind you, I'm not sure changing things to allow moss over steel helps very much. Consider a level like "Over the Hump" (Daunting 24). This is an earth-terrain level where steel had to be added to prevent the player going straight through the terrain. It doesn't look good. It looks as if the steel is separate from the level instead of an organic part of it. But I don't know how one would improve on this within the Lix (or for that matter, Lemmings) build-up-level-from-terrain-pieces paradigm.
To return to the original question: on first playing Lemmings, my automatic instinct was to regard terrain-on-steel as a form of layering, and to expect that explosions would leave it intact, just as terrain can partially obscure water, but when you remove the terrain, the water is still there.
I accept the point that if terrain-on-steel is allowed to behave as steel, then some information is hidden from the player. But that's true of water also, and it's often desirable to allow terrain to partially overlap water for aesthetic effect. This has, in a couple of cases, led to problems where the designer has let the water extend too far under the terrain, so the player expects a certain area to be safe to excavate and it turns out to be fatal. But we can discourage this via forum feedback, rather than changing the game engine to make it impossible.
Moss on steel rarely hides
important information. The rest of the steel block is still there, so the player doesn't start thinking "Perhaps I can explode the moss, get inside, and bash through the rest of the steel." Well, they might think that
once if they're used to L1 glitches. But after a bit of experimentation, the player quickly finds out that Lix doesn't have those steel glitches any more.
I'm not sure where I'm going with this line of thought any more
I should probably come back to this some time when I'm less tired.