That's a bit misleading. It's like saying i can blow at a pressure of 16 psi in the void, but when I blow into a balloon whith the atmospheric pressure of the environnement, I can only reach 2 psi. The 16 psi is purely theorical.
That seems like a false analogy. In the case of thermal radiation you actually are emitting photons with a total power of 800W independent of your environment.