Some interesting thoughts. It made me think that each of these can mean the same thing but really they describe the level of detail that is involved with each.
skin - this changes the look but is an overlay (like putting a large sticker with cutouts over something)
theme - this has more granularly and lets you adjust parts of the look independent of each other (like your computer desktop "themes", they look different and can be further customized but the items you see aren't moving or being modified or changed)
layout - you can change anything and everything. not just colors, backgrounds, etc. but what is shown, where it's shown and how it's shown.
Layout makes sense to me. I just don't understand the forum terminology being disjointed from the program it supports. Like I mentioned earlier in the thread even making it "Themes (Layouts)" would help new comers. Attract-Mode doesn't have a ton of documentation so the forum is where people go second (first in too many cases) to find answers.