I agree that they would be bad investors if that was their only criteria. But most investors (and in fact most consumers) are heavily influenced by social proof.
Have you ever bought a certain article over another one on Amazon because it had great reviews?
What a feature by TC is saying, this startup is interesting enough that TC wrote about them. It is a sort of a filter, much like YC is one.
Being written about on TechCrunch can also help create a sense of urgency with the investors you are already talking to, because now there is potentially more people interested.
