There are some reasons to look for the next step in your career, regardless of whether or not it is with the same organization. The first is blocking. If there are people with less seniority below you, you staying in one place may be denying them promotion. Second, some companies have fixed-step pay scales, and once you hit the top, you might only be getting cost of living increases from that point forward.

I fully agree that not everyone should dutifully stomp up the corporate ladder. A lot of us like "being in the trenches" and not having our week filled with meetings. We just want to work and keep things running smoothly.