I do think that some parents just have a higher tolerance for whining and crying. It may also be the case that the parents have been reinforcing manipulative crying (and the kids have been negatively reinforcing parental capitulation) for so long that it becomes hard to break.
It's easy to give into a kid occasionally in the short-term if you're busy or stressed. Once you've started down the path of partial reinforcement, the crying/tantrumming is often particularly resistant to extinction. Even if you muster the will to stop reinforcing it, you will have a period of intense crying/tantrumming (
extinction burst) to look forward to that can be hard to endure.
Boy! I'm chock-full of jargon today!
I've never tolerated what I considered manipulative crying in my kids. So, I don't see it much.