well you don't know that, the price has gone up steadily each year.
as EG says, they have done incredibly well in the current climate, though a lot of similar hobbies that might be stereotypically viewed as big boys toys, such as Hornby, airfix, radio controlled vehicles etc. have all proven fairly recession proof at the moment. middle aged, middle class men with disposable income have driven a lot of sales. I was in my local hobby store just after Christmas a a guy was looking at a radio controlled helicopter, he asked how much it was, staff said £450. wife walks out looking horrified, man nods and goes 'hmm very nice, might get one of those.'
Privateer Press' plastic models are resin too. technically, chemically etc. yes they are plastic, but a very different thing for hobbyists, and not nearly as good to work with as GW plastic.