It's called copying, and it happens all the time in China. They do not follow the same copyright standards that you see in much of the rest of the world. It's pretty much do whatever one can get away with.

For example, I've got a WM .45 size P-51. As a bit of experiment I bid on and won a similar size P-51 off eBay. When it arrived I found that the size, shape, and design was nearly identical to the WM P-51. The finish was ok, but not up to WM standards. The instruction book was the same too, although it was obvious that it was several copies away from the original. I know what factory in China made the clone, and I know it's not the same that makes WM. So, while it's possible that GSP gets some planes from the place that makes WM, it's doubtful. Most likely, it's another plant in China that's riding on the success of someone else's work.

One more thing, have you read this thread? http://www.rcuniverse.com/forum/fb.asp?m=2350405