LBE – minimal balance changes for Heroes V 3.1.

There is definitely some logic to it, especially when we talk about passive skills like attack and defense, which constantly prove their worth. But as Nargott said, each skill has its own time.
I think taking this fact into account is also an interesting part of the development strategy, and even if you decide to take machines in the late game (note that no one forces you to do this), the machines will still pay off in the early game (a very important stage for any scenario).