Let's say you cover the next Twitter or Facebook before they become the next Twitter or Facebook. Once they explode in popularity, are you going to stop writing about them? Even though those articles are getting the most traffic on the site? And tons of speciality sites start appearing just about Twitter and Facebook. And you even know people from Twitter and Facebook since you profiled them when they were little, and can get the inside scoop on changes and upcoming features.
If they really would drop startups that made it big they could make it a feature. Instead of a deadpool, they can add startups to a bigpool, and tease the major sites with it: "we followed them then, you follow them now"
How does MacRumors decide when they are going to do another story on something that is hot?
I will check with my boss/editor and see what his thoughts are on the subject...