Thanks for chasing that down in detail! I had already started to think that when look some gardening question up in more than one place, I get differing answers. But you made it scientific!
Maybe some information truly is variable and depends on too many things to quantify easily, like height and bloom size.
I think other answers come from someone who tried it one way once, and the plants didn't die, so now he's an expert and knows the One True Way to grow something.
If I change two practices at the same time, and the plants stop dieing, I probably pick one of those things randomly and decide that was what made the difference and must be important!
Maybe some companies know that they have to list SOMETHING under "cultural advice", but their budget for getting it right isn't enough, so a lot of copy-and-paste is done.
