At the moment the ripple network has a lot of isolated disconnected nodes. It's not enough to distribute initial XRPs, one must also ensure enough incentive for people to connect to each other and to establish at least minimal lines of trust in their local currencies or BTCs.
Why not do a cascading distribution where people get an initial allocation for simply signing up, solving a CAPTCHA and verifying their email by clicking on a link and then they would get additional bonuses over time for connecting out to friends and family ?
For one thing, this would allow people to sign up for as many accounts as they can create email addresses, and receive XRP for each of them. Second, connecting (extending trust) to friends and family is not necessarily desirable, and it shouldn't be encouraged unless you have a good reason to do it.
Simply requiring aged gmail or yahoo accounts helps prevent multi account sign ups, similar to how only aged bitcointalk.org accounts receive the giveaways. Gmail had referrals by friends in its beta early access period, same can be done for ripple accounts, this would just create some scarcity for them at first. Encouraging connectivity in the long run is desirable to create viable paths in the network, for now that maybe deferred.