Regarding the best connected category -- lawyers eventually move up to become partners, who are rainmakers. Their job is to bring in deals and manage the client relationship, rather than drafting the paperwork. The work is very different from that of the associate level.
WSGR takes a mix of top 5 law school grads as well as Santa Clara law school grads. The latter is seen as having a better local network through their family and upbringing (and have a better retention track record compared to their higher academically ranked counterparts), and are seen as effective future rainmakers even if their legal abilities are inferior to their peers.