If I were in Techcrunch's shoes, I wouldn't link to tweetknots because I wouldn't want to give press exposure to a site that brazenly copied its design, css & images from Twitter.
I'm a pretty big Techcrunch hater (and the idea of TC refusing to let someone else benefit from drama-mongering is funny), but I think not linking to tweetknots is a defensible decision.
Twitter did buy their images from a stock photo site and they didn't buy the exclusive rights to the image.
Everybody can buy the start site image and can run his own site with the same image as background!
I'm a pretty big Techcrunch hater (and the idea of TC refusing to let someone else benefit from drama-mongering is funny), but I think not linking to tweetknots is a defensible decision.