Sorry for misleading you, that certainly was not our intention. As you can see, those forum posts are more than 2 years old. We try to maintain accurate information in all of our marketing material, and I don't believe we state that we use GPU computation anywhere aside from these forum replies, which were true when written (I just removed the irrelevant information from the Linux troubleshooting post).
We are an Early Access game in active development, and features are bound to change. As our physics developer said in that quote, we once supported this, but CPU implementation proved the better path for now. Our new "Native Physics" on the CPU is actually much faster than our old GPU implementation ever was, mainly because more of the code runs on fast C++, where previously only the gravity actually ran on GPU, while everything else was on slower C#. It's possible we'll be able to move to some GPU computation again in the future, but so far it's only been an improvement on our old system.