A change from a state of non-power to a state of power requires the wielder of power to accommodate those changes; power may corrupt - then again it may not.
The observer who judges usually observes from the position of non-power, so he or she may draw conclusion from a single, limited perspective.
The phrases "power corrupts" and "absolute power corrupts absolutely" do not hold much accuracy in regard to individuals; changes are necessary, but the question of whether they erode the integrity of the individual cannot be answered in general.
Systems, however, are a completely different story.
Power attracts individuals who desire/hunger it - many of those are willing to sacrifice their integrity to obtain more power.
A system is not static; individuals come and go, and the system itself fluctuates. If the system gives the promise of power over others, those who are corruptible tend to stick around.
A corrupt system works by dispersing responsibility/accountability - no one knows who does what, and those who know won't say. It is a playing field open for unscrupulous manipulations.
Thus, even a transparent system with a not-so-good structure will necessarily become corrupt.
In conclusion, for systems the phrase "power corrupts" holds much accuracy - if a system can be broken/abused/corrupted, it will be.