10KLOC is not a reasonable argument to open-source everything in the world ever. I'm not surprised that OS has a lower 10KLOC than proprietary simply due to the number of developers available to optimize code. But so long as the code itself works, then fair enough.
My argument is that open source developments are usually, simply in my experience, either software not worth charging for or you couldn't charge for. Most proprietary software is such that you can charge for it and, given the scale of development, you should.
I have to say though, the tone of argument against what I'm saying is strikingly similar to suggesting to someone that illegally downloading GBs worth of recorded music is in some way criminal and/or morally wrong. I have personally seen artists who have attacked music pirates drawn over the coals at the mere suggestion (e.g. the lead singer from the band Terror).