I'm looking at publishers who do release Linux games using internal engines. Most of them use binary or source wrapping. Only a minority are implementing proper native rendering in those engines. And I bet it's based on cost considerations like I said above. How would you explain it otherwise?

And I'm sure that cost plays a role when small market is evaluated. The higher is the cost, the less likely such publisher is to care, because prospects of profits are also reduced. So it goes back to my point. Lock-in proponents like MS and Co. benefit from lock-in in slowing down competition growth.