History plays a massive role.
Consider the different states of different motors by the time they're second-hand. Different octane, different oil, different driving style and road conditions. How cold were the cold starts, and how frequent? Clock up 100,000km on several identical cars with different drivers and you'll have several different motors.
Just like some TTs will chug on forever (like JoKer's and Drunkenmonkey's), others will let go with very little provocation (Reuben's), or none at all (chrisjunkie's). Some come to us already rebuilt because of past bearing failures (Jasn00's). Out of all those we have 4x EJ20Rs and one EJ206, in varying states of modified or not. All the 20Rs are in GTB-Ltds in the above example. Oddly enough as far as I know, the two white ones are stonkin' on like there's no tomorrow but the other two have failed and since been replaced.
My personal feeling with that particular EJ206, given how cheap the car was and in what state it was delivered - despite being completely and utterly stock - it had been poorly maintained, and Chris' loving maintenance of it in its first 3 weeks under his ownership had successfully flushed out the sludge that was once oil...including the sludge that had been holding what was left of the bearings together. It made the magic nugga-nugga sound not long after that service...
History... past driving conditions and maintenance... play an enormous part in that big equation. This is why there are no absolute answers, just strong recommendations. Some are stronger than others. It pays to listen to the wise old hands here.