I think he is reffering to the other side of the file (rough) my guess is that its case hardened and LM are banking on 99% of people not using it enough to wear out the case. I would say the odds are with them. This way they can stamp out the saw parts, case harden them in one huge batch, glue on a bit of diamond dust and slap it into a tool.
Note that wearing the file out (including the diamond side) is covered by their 25 year warranty. Either way (W-1 or case hardened) you can't really lose.