Seriously: Facebook gets network effects from having users network with each other, as it learns about the connections between people and can improve their social graph. Facebook aggregates a lot of complex, contextual interactions with how people relate to each other: family, spouses, love interests, college friends, elementary school friends, colleagues, etc. Twitter is all about three things: followers, following, and lists. Twitter lists are limited: you can only have twenty of them. Twitter is working with a sparser set of data [fewer variables], and for that matter, data that requires greater inferences. If I list Rick and Jessica as people I’ve known since high school, it can be surmised that there’s a stronger bond there than … well, how do you determine any bond’s strength on Twitter? Furthermore, even Facebook doesn’t know that I was the best man in R&J’s wedding—not even if we start posting photos from the wedding itself. [If it can, well, it's sentient, and then I gotta take drastic action.]
One can draw inferences about networks on Twitter, of course. You could look at the concentration of, say, Whiskerino alumni and figure out, eventually, that all of us know each other somehow. You’re going to better understand this, however, with a list. I get that Twitter may be trying to draw more information about the interactions between its users, but “features” like Who to Follow generally just end up pissing the very people who’d help grow your network off. On that score, count me in with Derek.