This is relatively well known in (Complex) Network theory as applied to Social Networks. You're always more likely to be connected to a Hub (someone with high degree) that to a "leaf" (in the tree sense). If you plot the average number of friends your friends have versus the number of your friends on a log-log plot, you'll see a decreasing line. (See Fig. 2 of <a href="http://arxiv.org/abs/0909.0450" rel="nofollow">http://arxiv.org/abs/0909.0450</a> for a recent example).
It looks like the only difference allowing for more friends is that those people are specifically more likely to befriend people with fewer friends. (Sue and Alice, in the example.) One could take away from this that the secret to having many friends is to excel at befriending those who don't make friends easily. In some cases, you may be the only friend they have.