Superdelegates come in two basic flavors: democrats elected to national office (representatives, senators and governors), and members of the party ("Distinguished party leaders", DNC superdelegates and just 4 congressional delegates). Obviously, the first group has to answer to their voters, while the second is free to "vote their conscience".
There is a huge disparity in the way each of these blocks is endorsing candidates.
So far, according to politico.com, elected superdelegates are 92-83 for Clinton, essentially a tie (52.5%-47.5%). But unelected ones are for Clinton by an almost two-to-one margin, 154-88.5 (64%-36%).
Certainly, not all elected superdelegates are endorsing based on the vote of their constituency (for example, both senators from WA endorsed Clinton and both senators from MA endorsed Obama). But it seems that this group as a whole is unwilling to go against the popular will, unlike the unelected party insiders.
Number collected from
http://www.politico.com/superdelegates/ .