I largely agree with your sentiment but I think it's important to consider that with our current government it is not reasonable that we should expect them to adhere to election manifesto promises.
We have a coalition government because no single party was elected with a majority vote. The government results from a compromise between the two parties and thus their election manifestos should be considered void.
It's because of this that I feel a little sorry for Nick Clegg over the student tuition thing - the public have held him accountable for a promise that should be considered void since he wasn't elected.