Pine wood floors on 2x4 risers?

[Justin Fox]

I'm redoing my own kitchen right now and in the process of tearing up the wood floors in the kitchen.  The previous owners tiled over the wood but sucked at everything they attempted to do.  Anyway.  We tore up the tile and hardie, then started to tear up the wood and it's suspended by 2x4 risers and the 2x4s are set into place on the concrete with tar?!  I've never heard of this and wondered if anyone else has?  They also had a plastic moisture barrier laid down, but over the 2x4s (directly under the wood flooring.  If you were going to do such a thing, wouldn't you put the plastic directly on the floor?

Thanks,

Justin