I'm pretty certain people know that; and that their income from them is affected like anything else
The difference is that OKW cannot build them themselves, so OKW with OKH teammates are much stronger than OKW by themselves
That's true, BUT in small games (1s and 2s), the poor Ost player should spend 200 MP, and they are already MP starved, so Ost player should sacrifice a units for fuel income. But, imagine of OKW player-with their unspent MP pool-will be able to build caches. So the Ost player can also benefit from this while saving his MP for teching/units.