How would you define ruthlessness I guess? I mean, I can name a lot of YC startups that are crushing their competitors by relentlessly making better products. From my batch alone there is Disqus (whose product is significantly better and gained much more traction than their closest competitor, Intense Debate) and Dropbox. They've both taken a lead over a field of entrants in terms of innovation.

I mean, they haven't thrown any bricks through their competitors' windshields, but they haven't passed up any chances to make their competitors look half-baked.