I don't think you can blame people too much for taking the Government's leaflet at face value.
I see what you mean but I think it's the understanding of what 'Government' means that's the issue.
Most of us think of 'The Government' as being the people in charge of the country - the 'establishment' if you like. Reading between the lines it seems that it's a complete shock to some people that the Government can't just decide things and they happen, it depends on them being able to get them passed through Parliament on a majority vote.
Often the Government can rely on their majority to pass whatever they want through Parliament but it's by no means automatic - and that seems to be what people aren't grasping here.
Apologies for stating the bleeding obvious above but there seem to be a lot of people around who are suddenly interested in the mechanism of government and politics, when they only paid it cursory notice before.
I'm trying to think of parallels between the Government-issued leaflets and booklets 'promising' that they would implement the outcome of the referendum and other leaflets issued by the Government and their various department.
My mind's gone a bit blank on individual examples but I know there have been many times in the past where Government leaflets and advice on various subjects - from Income Tax to speed limits to benefits claims to VAT etc. - have been at odds with the actual legal position. Isn't this just the same thing?
Do we take Budget documents at face value for example? If the Budget Red Book (hope I got that right!) says "we're going to [whatever it was that they backed down on and then fudged]' and then there's either a popular uproar or the required legislation doesn't get passed, do we call it a subversion of democracy if the Government don't fulfill their promise? We don't, it's a pathetic administrative fail, that's all.
Excuse the rambling post, I'm a bit tired and emotional. 