There's a case for viewing commercial public relations as the 'acceptable face of capitalism'. Championing an organisation's responsibilities to all its stakeholders balances the pressure always to put shareholders and profits first. Corporate Social Responsibility and environmental statements play their part in this.
Contrast this with party political public relations where there is a long tradition from Bernard Ingham to Damian McBride via Alastair Campbell of the PR adviser as chief 'attack dog' for his (my examples are all male) political boss. The unacceptable face, if you like, of public relations.
Why such a contrast between the corporate and political worlds? David Starkey, I imagine, would talk in terms of courtiers and princes. The political PR adviser is a courtier whose power comes solely from their close proximity to the prince, hence the need to take risks and retain the favour of the ruler. Call this the Machiavelli theory.
Politicians, in a democracy, stand or fall by their electoral success. So successful politicians tend to be an everyman (or woman) causing least offense to the electorate (and the Daily Mail). Maintaining an inoffensive public persona requires some strong arm tactics behind the scenes and (unelected) courtiers are more expendable than political princes.
Private sector bosses do not have this pressure to stand for election; they are undoubted kings of their courts. Yet they know they are accountable: to shareholders for profits, to employees for strategic leadership, to customers, regulators and communities. These various accountabilities need careful balancing, the role of corporate public relations.
PR Studies 
Having done both, I’m not so sure there is such a huge difference between political PR and corporate PR. The media focus on the tip of the iceberg (the attack, sleaze type stuff), but the vast majority of work is quite mundane and simiar to the business world – researching and writing articles/speeches, organising events, messaging, responding to interview requests etc.
Lots of thoughts on this post!
1. The media are surely complicit as they feed from the juicy stories of the political spinners.
2. The use of propaganda to put forward a single point of view or belief can work in organisations as well as politics.
3. The makers of the new film “In the Loop” must have thought the McBride story was manufactured to give the film publicity! Fact stranger than fiction?
4. Intimidation and bullying seems to be endemic. We shouldnt be surprised if it surfaces in political PR – but we shouldnt accept it as inevitable either.