The PDP-11 postincrement thing is very often repeated, and I'm sure there are good reasons to suspect it, but here is one bit of evidence to the contrary I find convincing
Nisan and Wigderson prove many different corollaries of their construction in their seminal 'Hardness vs Randomness' paper but their requirement for general derandomization (P = BPP) is that there's some function f computable in time 2^O(n)
such that for some e > 0 for all circuits of size 2^en the correlation between f and the output of the circuit is sufficiently low (if I understand correctly).
https://yarchive.net/comp/c.html