What's the deal with AI planet capturing?

[Q]

Rollo I can confirm your obsevation that the AI attacks the least defended colonies in a system. I was under attack of 4 fleets with up to 90 ships in a system with 12 colonies, some but not all of them heavily protected by defense bases, weapon platforms, several hundreds of fighters, hundred satellites. The AI did not attack the well defended colonies but whiped out the weaker ones, exactely as a human player would have done it. The AI never lost a combat, when attacking a colony. I could only stop it when I had a fleet large enough to attack his fleets.