the Linux process for generating many rare flaws

Quite so. I suspect this will always be true for something like the 
kernel. In a sense it's true even for perfectly reproducible systems like 
compilers, but with the kernel, half the things can't have testsuites 
because they require specific hardware, and the other half can't have 
complete enough testsuites because a lot of the bugs are races or 
otherwise timing-dependent and can't be reliably reproduced. (The mm 
subsystem is a classic example of the latter.)

Filesystems can *probably* have good testsuites, but I'm at a loss with 
respect to most of the rest.