Hi
Most likely what you are seeing is not a clear coat but 'polished concrete' which is a process of progressive grinding of the floor with large grinder machines and multiple passes of finer and finer diamond pads, and the addition during the process of adding densifiers and stain blockers that get burnished in. These are very nice floors, easy to maintain vs VCT but are not very chemical fluid resistant so hence not recommended for garages. Many of the national chains are converting to polished concrete due to it's neutral color and high-wear characteristics and reduced maintenance. The level of sheen is controlled by how many steps of polishing are performed and can range from a satin/matte (#200 diamonds) up to a mirror finish (#3000 diamonds).
Also they are cost prohibitive in smaller spaces due to the equipment needed. The darker lines come from years of cleaning with cleaners that have residual dirt in them and the dirty water leaks through the tile joints and soaks into the floor, and there is no easy way to get rid of this as the depth of the stains are beyond the few thousandths of an inch that is removed during the polishing process. Many people like the 'industrial' look of these floors also.
Our clear SPGX Polyurea achieves a similar look.