I don't see the frustration so much about job security as about not being able to really get the most out of a technology before it becomes obsolete. It's one thing to be able to simply use some technology to get the job done. It's something else to deeply understand it and to become fluent in its paradigms and write code that is idiomatic and elegant. When a developer has to spend half the time learning new frameworks, it isn't so much about the loss of job security, it's the loss of craftsmanship.
