Management is different. Managers don’t micro-manage. They trust engineers to make the right decisions. Trusting employees changes the role of managers at Google from what most folks envision when they think of management. In addition, managers can’t unilaterally, hire, fire, or promote. Many of the important management decisions that could be perceived as office politics are handled by a committee to remove that danger.
You may not see web development and software engineering as different positions. Both involve programming and craftsmanship, but software engineering adds to it knowledge of data structures and algorithms, compiled languages, memory considerations, and understanding the impact of coding and architecture decisions on the machines where they reside.