"Lead" implies taking the largest position in the round, often but not always around 50% of it. VCs typically have a strict profile for the size of check they write -- though I think this is more prevalent at the seed stage, where funds top out pretty quickly at fairly small check sizes. I think the dynamics are probably very different from this at later stages, but then again the article (and all this discussion) is about seed funding, as far as I can tell.