Yeah it's a rule of thumb not an iron law. When looking at a lot of bikes at once and quickly, the turkey lever/ dork disc/ stem shifter test may occasionally cause a false positive for crap, but it is still a good way to quickly narrow the field of candidates. The average bike without these features is going to be much nicer than the average bike with them.

Of course this test can also focus your eye on less conspicuous signs of crap on the bike such as steel rims, cottered cranks and a sticker that says "hi-ten".