This article is spot on, albeit was written before the decision by the Obama campaign was made.
By seeing what happened in the 1992 Democratic Convention with Bill Clinton, Jerry Brown and Paul Tsongas, the strategy and even the traditions of political conventions illustrate proper protocol. It shows how clearly the Obama campaign thought this through:
...the case of the ’92 convention illustrates the absurdity of the should-she-seek-one-or-not debate over Hillary Clinton and a roll call. It really doesn’t matter what she does.
Let’s say she does what Tsongas did (at the Clintons’ insistence) in ’92 and releases her delegates, urges them to vote for Obama as a sign of unity, and refuses to be formally nominated. Even then, there’d probably be a roll call. Why? Because the only other option would be for Obama to be nominated by acclimation. But if the Obama campaign ever tried to gavel that through, it could produce a humiliating television clip, since a good chunk of Hillary’s delegates (a quarter? half? hundreds, at least) would angrily resist, believing that they were being denied their chance to express their voice. The idea of nominating by acclimation is to demonstrate that the convention is in agreement on something. But if hundreds of Hillary supporters were to scream in opposition (perhaps louder than Obama’s supporters), the effect would be awful for the Democrats.
This is one reason the Obama campaign is likely to seek a formal roll call of the states no matter what. The other reason is tradition. Delegates (and especially the state delegation chairmen and –women, who get to announce their tallies) relish the moment their state’s name is called, when the whole convention and the viewing audience on television gets to hear all about their state’s natural wonders, native products, and successful sports teams.
And if there is a roll call, then delegates can vote for Clinton whether she’s been nominated or not. Again, the ’92 example is instructive: Tsongas, by order of the Clinton campaign, released his delegates and requested that they vote for Clinton. He also refused to be formally nominated. And yet he still tallied 209 votes (just under half of what he won in the primaries) during the roll call.
http://www.observer.com/2008/politics/it-doesnt-matter-if-hillary-nominated-or-not