Right below the picture it says:
The mine (power value 1) and the connecting blue-circled
satellite are not needed to reach a power value of 7. The redcircled
satellite is sufficient to achieve this.
Since you only need 7 power, adding an extra Mine for an 8th power with an extra satellite is not allowed.
The 1st example shows that you could add an unneeded structure because it uses the same number of satellites.
See this topic for in depth explanation...