[toyg]

Could it be that over-1m-LOC proprietary projects are, in fact, fossilised? Once a project is large enough, deep changes are discouraged because their cost (and risk) to the business gets too high.

Meanwhile, open source projects like to refactor (somebody would say reinvent the wheel) forever and ever, constantly ripping out old code for new, so defect density is stable and simply rises in line with overall complexity (which obviously rises with project size).

I'd be curious to look also at developers' turnaround rates: once you leave a company you can't keep hacking on their code, which is something you can actually do with open-source. As old developers leave, their code lies untouched for fear of breaking anything, and again gets fossilised.

[sliverstorm]

You could probably also speculate about the impact of the corporate projects. For example, if the project is over 1M LOC, can we surmise it is very likely that project is their bread-and-butter (and thus gets much more attention and resources)?