Well stanton, I TIG weld every day for a living. I will conceed that it was poor wording for me to say that the ARGON is doing the cleaning, even though I believe the it plays a large part in keeping contaminates out of the weld, even stuff that is left on the metal post cleaning. My teachers taught me that going over the weld prior to actually laying a bead, can help keep contaminants from the weld. I do not heat up the area enough to puddle just quickly go over it and then usually grab a wire brush and clean again. Many times the heat will draw oils to the surface (especially in cracks). I'll keep doing it that way because it works for me. I weld tool steel mostly that have been run in a stamping environment. We do our best to clean the steel before welding, however cracks etc. hoard oils and dirt that we can't get. I'm very familiar with cantaminated welds, and have on occasion had to grind it out and redo it.
Also, try welding aluminum with AC. Then you'll have the natural CLEANING effect of alternating positive and negative ions.