I would suggest that you read part 141 of the FAR's if you want to find out for yourself (and part 61 also)
1.) it explicity says that applicable subjects of the AIM must be covered in a private pilot program.
2.) as PIC you are responsible for knowing and complying with the FAR's.
those two things alone disprove the bs you thought you read.
However, what you read might have been applied to wx and other set minimums.
ie. if it is marginal weather, you shouldn't be doing pre-solo training with a new student, although technically, according to the FAR's, you might be doing it legally...
I think that's the case, they are telling you to be "safer" than the FAR's require, and not pushing the envelope (cloud clearances, decision heights, et al). I certainly don't think any author would be ignorant enough to write that you shouldn't own a copy of the FAR/AIM before you get your license because the FAA discourages it.