4. A system that never needs to scale much beyond its original projected load.
First read as "original project lead", but I think that could apply too.
That's certainly true in my experience. I've seen some great, readable, codebases written by solo developers that had lots of previous experience writing code in larger teams.
Caveat: it's never something that's too large or complex, of course.
While true, in my experience this usually happened when at least one - if not all three - of these conditions were true:
1. The problem domain is relatively static, unmoving, and self contained
2. The systems in question is relatively small
3. The developers in question have written substantially similar systems before, or ground locally, or used version 0.x version numbers first (in any of these cases, is it really "version 1" per se?)
...game development is admittedly weak in all 3 categories, and high on time pressure. Oh sure, there's some solid code that will probably last decades in many codebases, but even the best programmers will occasionally make a system that - while good in isolation - needs reworking when combined with other systems - to say nothing of the content and rendering pipelines that vary wildly by decade.