The first file and the last file are saved as autocad 2007 format. They are more or less the same thing, just the web one liked adding a decimal point to everything for no clear reason, e.g. 0 becomes 0.0 and 1 becomes 1.0, bumping up the file size.
It appears that it heavily records things in “Splines” while the older format records in vertexs (small straight segments)
Edit: On furthur reading, Kicad does not support splines at all, It may be added later, but for now that is what is preventing its import.