They are still part of the coalition though, and if those pledges dont mean anything since they didn't come first then how are those pledges worth anything in the first place? Are they just bargaining chips?
Their manifesto pledges are made on the proviso that they are elected to power. They were not so their pledges are not able to be enacted without the support of the other parties.
They chose to go into a coalition to support the Conservative leadership and thus they have to compromise in those pledges somewhat, which is what they have done. No one has been duped or used a bargaining chips, the students who voted should have looked at the manifestos and the likelihood that they would be elected to power in order to enact the pledges therein.
No-one is to blame here, economics has forced a decision which it turns out is actually better than either the status quo or the alternatives of a graduate tax or fewer available places.
Unfortunately for whatever reason the NUS and associated bodies were under the erroneous and somewhat naive impression that the Liberal Democrats had enough influence to scrap tuition entirely and no matter what option was put forward they would have encouraged the demonstrations against anything less, as they have done.