Founder Control
Perhaps the ycfounders list is a selected sample: it produces or selects above-average quality founders that are more likely to get a good Series A price (in terms of both control and pre$).  I suspect that YCombinator's focus on founders for investment decisions also results in start-ups with assets closely tied to the individuals who run things (rather than say a patent).  This leaves future VCs with less bargaining power when forming boards.