In my defense, I never saw your smelter when I made my original - I saw cr15py's, and therefore gave him a thumbs-up for the idea. That being said, expecting and requiring a shout for an idea that's been around for 8000 years is silly, to say the least.
tl;dr version in last paragraph - the rest is a short analysis of the designs mentioned.
Now, let's take a look at five of the six smelters: http://www.etmoonshade.net/rconoverSmelter.jpg The original design in question. The mixer is bloody brilliant, although the amount you can smelt is a bit small (imho.) I never saw this version until I poked at this thread.
http://www.etmoonshade.net/PetakiSmelter.jpg An incremental improvement over rconover's design. It's obvious that it's at least a copy in part, since the elements are the same. That, and of course the fact that rconover's name is on it. I didn't see this one until a fair bit after cr15py's - at that point, I already had the basic design of the smelter in place, and was just tweaking.
Crippledfaggot123's smelter is another incremental improvement, adding something to catch and cool the smelted metal. I didn't bother with a screenshot.
http://www.etmoonshade.net/cr15pySmelter.jpg cr15py's smelter is indeed the same sort of idea as the ones above. You use a rectangle (the easiest shape to make in PT) to house the thing, heat the material up, and use switches to control pouring. At risk of alienating cr15py (who has already stated his appreciation at being mentioned,) the mixer isn't all that great, the cooling is a little bit off, and bits of stuff get stuck inside the mixing chamber. If he was copying you, wouldn't you think that he'd choose some of the good ideas you used? :P
http://www.etmoonshade.net/themadscientistSmelter.jpg Obviously a recent design given the use of NBLE, it probably takes some ideas from previous designs - comparing and contrasting the screenshots though, they're just that - ideas. The rectangular shape is once again an obvious "innovation," and the mixer is quite nice for something with no "moving parts". The use of the NBLE for heating the metal, though? Nice. ;)
http://www.etmoonshade.net/EpsilonSmelter.jpg My own submission to the smelter craze. My innovations in the whole mess are the use of a switch to start the cooling, and two seperate chambers for two different materials, allowing the user to have equal amounts of each material. It's distinctly possible that I was influenced by Petaki's design for the placement of the white holes (on the top,) but that seems once again to be fairly obvious - you need to generate pressure, you put the pressure source near the thing you need to pressurize.
tl;dr version: I never saw your work until this thread, rconover. Looking at the smelter designs, your idea of a smelter may have influenced each one (either directly or indirectly,) but I fail to see any actual unattributed work in -any- of the designs you mentioned. I'm not a mod, so obviously I'm not the one who makes the decision on what is and isn't stolen - but I don't see what your issue is with the designs other than maybe a feeling of ownership of the concept.
We could implement something like this: UBGC(Use but give credit): you can save stamps from this and save your own copies of the sim publicly, but there will be a small watermark at the bottom corner with the creator(s)'s name PDC (Play, Don't Copy): You can play teh sim and mess around with it, but if you copy anything from it, you can't save it publicly FTD(Free to Distribute): no copy protection exists.
Maybe A new feature should be added which disallows stamps to be used on the creation. You can load but no t save, and it would be a box like the public/private selector