jumbojohn: Just what is the definition of a slippery or contaminated runway?
If my memory is correct, Slippery-Wet data is used when something on the runway is a factor for stopping, but not so much for accelerating. Typically this could be a thin layer of water on a non-grooved runway, ice, or compact snow. The data varies from one airport to another, and from one runway to another.
A cluttered runway may be snow, slush, or standing water. This affects both stopping and accelerating performance. The depth
and type of clutter is an important discriminator.
I think both can be called contaminated, but they have different effects on takeoff data. Additionally, crosswind limitations change based on the state of the runway.