We can split hairs about whether a material is strictly speaking plastic per se, but we can not argue that loosely speaking it very definitely is a plastic material. For those wanting to chase the answer (strictly speaking) take a glance at what wikipedia say here: http://en.wikipedia.org/wiki/Plastic
When you look at the history of plastic, you can see there a some similarities to the material bakelite (phenolic). I found some parallels in this:
"Baekeland found that mixtures of phenol (C6H5OH) and formaldehyde (HCOH) formed a sticky mass when mixed together and heated, and the mass became extremely hard if allowed to cool and dry.
...He continued his investigations and found that the material could be mixed with wood flour, asbestos, or slate dust to create "composite" materials with different properties.
...Phenolic plastics have been largely replaced by cheaper and less brittle plastics, but they are still used in applications requiring its insulating and heat-resistant properties. For example, some electronic circuit boards are made of sheets of paper or cloth impregnated with phenolic resin."
Which leads us to fiberglass:
"In 1939, IG Farben filed a patent for "polyepoxide" or "epoxy". Epoxies are a class of thermoset plastic that form cross-links and "cure" when a catalyzing agent, or "hardener", is added. After the war they would come into wide use for coatings, "adhesives", and composite materials.
Composites using epoxy as a matrix include glass-reinforced plastic, where the structural element is glass fiber, and "carbon-epoxy composites", in which the structural element is carbon fiber. Fiberglass is now often used to build sport boats, and carbon-epoxy composites are an increasingly important structural element in aircraft, as they are lightweight, strong, and heat resistant."
While I certainly don't profess to having the science background to claim anything with absolute certainty here, I do feel safe in saying that most people that see the Xd and Classic series cabinets would agree that some sort of plastic material is being used in their construction. That is not to say plastic cabinets are bad thing, just that there need not be a correction interjected whenever the association is made between these cabinets and the (in my view) aptly applied plastic description.