There is also the question of what is being conserved; it may reflect the history of each individual's exposure to particular concepts more than the history of the field as a whole. One might even argue (pace GKC) that many ideals in CS have not been tried and found wanting, but have been found difficult, and left untried. E.g., the idea of writing a program as a largely stateless nest of expressions interspersed with delimited groups of statements goes back to 1960's CPL, at least. Von Neumann's 1945 formal methods were actually a bit of an advance on what Floyd (who did say he was just writing down some folklore) popularized much later. Model theory may be contemporaneous with Turing, but Universal Algebra predates him, and so the example plea that "boolean operators produce only booleans" sounds to me (as someone who prefers J's model in which boolean operations are all special cases of more general ones on boolean domains) like a call to return to the good old days of the XIXth century.