There will always be exceptions.
So yes, specialized therapy would be required for someone with rickets.
How many people do you actually know who suffer from rickets?
How many people do you actually know abnormally shaped bones?
"When all you have is a hammer, everything looks like a nail."
Pete Egoscue's advice will not apply to all.
Some may say that makes his advice wrong.
I'll bet his books and therapy have helped a lot - probably most.
And probably not harmed very many.
Hopefully Posture Guy, who is an Egoscue therapist who frequently posts here will weigh in.