If I was to judge by my habits, this stats can be really broken. The only option I use AddThis for is sharing by email. In stats it'd be that I share by email 90% of the time, while I use 'share on facebook' buttons all day long, and AddThis I got installed only to save clicks when sharing with people who are not on fb.
Could it be that websites like del.icio.us and StumbleUpon generally have better sharing methods already than e-mail, which is not as quick of a method? Sites that are dedicated to sharing generally have bookmarklets, browser toolbars, and other programs to make it easier, whereas e-mail is something that it may be easier to do with AddThis.
the trend I've been seeing (very limited view) is people creating a tumblr and sharing stuff through there.
i guess there's an opportunity to attack facebook around here.
people who create tumblr blogs usually are not only following people who they know, but mostly people they don't know.
since tumblr is not social network in the sense that you don't have to give them your private info, there's not much of a privacy issue.
you can follow random people and get followed back by randoms (but not necessarily)
you can also share all kinds of stuff you probably don't want on your facebook.
plus it's customizable with themes.
i guess it's myspace gone right? or maybe twitter/friendfeed for non-techies?
