Emotional attachment

How is it that so many people have experienced so strongly the attachment to this object? It’s totally passive and yet (wikipedia):

Jeep Barnett, a programmer for Portal, noted that players have told Valve that they had found it more emotional to incinerate the Weighted Companion Cube than to harm one of the "Little Sisters" from BioShock.

Is it the solitude, the sympathy with the secret prisoner, or maybe it’s only when they have a productive colaboration prior to the departure that people feel this kind of attachment? Well, maybe it’s just a joke… but not only is this video moving enough that I thought I had to post it but also it’s a good excuse to underline the importance of emotion, attachment in games. And here’s me getting back to my usual tune: please make this interaction and attachment a real one, one made with one’s own choices and decision. I can’t and will not feel personal attachment to a character that I’m only interacting with through cinematic moments. That’s as passive as a movie, not as powerful as a personal experience. Here’s to hoping more emotional attachment moments will surface in games!!!

PS: for those who’ve played Portal: this is trully an image that makes me laugh & warms my heart & makes me think at the same time.