cast iron coating?

i was in wal*mart last night and i saw lodge cast iron.  so, i looked at it.  on one of the pans, there was a bubble in the surface.  so, i scraped it off and saw metal pan underneath.  it looked like a black plastic coating of some sort.  it coated the whole pan.  is this normal?  is it necessary?  is it on all cast iron pans.  my friend used to have some and although it's been years ago, i don't remember that coating.