the eclipse models are a mixture of a wet-dry style (the biowheel) and mechanical filtration (the filter pad)
dont remove the carbon. If you would recall from chemistry class, carbon is the most reactive metal because of the number of valence electrons it has. it can gain or loose electrons to bond with jsut about any ions. and it is also very electronegative so it could take ions and charged particals taht are attracted to the H ions located in a molecule of water or the negative oxygen. So to sum it up, carbone removes toxins, organics, metals, most unwanted elements, ect.
as far as removeing stuff from the bottom of the tank as oposed to the top: Both have their advantages. If you dont have enough surface aggitation, or even if you do, up to 75% of dissolved organics are located on the waters surface and this can screw up your levels. This is why if you dont have a skimming divice for the surface, you should have a lot of water flow on the top.
But the advantage to having water being taken form the bottom or mid level range is taht if something is floating in your water collum, it wont be picked up by surface skimming. It will just hang out and your water could turn yellow and not be too clear.
This is why the new overflows for the AGA's have two sections, the inner most section acts as a normal overflow, the outermost allows some surface skimmering and it has slots in it to allow some water to come in form the water collum.