Many have commented on how Hilton got fed up with 'banging his head against the wall' of the staid Whitehall establishment once in power and endless compromises with coalition partners such as Vince Cable.
Hilton is that paradox, a thinker of the right philosophically, yet also an arch-moderniser who challenged old Conservative orthodoxy. He also deserves credit: his work on Cameron's image and policies in opposition were sufficient (just) to make his charge electable in 2010.
Cameron has now lost two of the 'inner sanctum' or 'Famous Five' with which he gained power, the first being comms director Andy Coulson. George Osborne and William Hague remain, of course. Craig Oliver has ably filled Coulson's shoes in Downing Street but Cameron will have more difficulty replacing Hilton. Indeed he hopes Hilton will return before the next general election, after recharging his batteries in California.
Already we are seeing a shift back to government comms orthodoxy, as this administration begins to spend again on large information campaigns, such as the anti-smoking work by Freuds.
Although government comms chief Jenny Grey still pays lip service to Hilton's favoured 'nudge' behavioural change theory, there is a sense that Hilton's original vision is being diluted. The chances are that hifalutin' concepts such as the Big Society will be quietly dropped as the administration accepts the harsh realities of office.
Just like any government, Cameron's will live or die on economic growth and jobs. And just like any other Prime Minister he will want to feel personally that he has changed society for the better. The latter can only be achieved by behavioural change, and ultimately by effective comms campaigns.
Any modern government must have a sustained constructive dialogue with its electorate, encouraging people to live better, healthier lives. The challenge is to harness digital and social media techniques, which are not only more powerful and democratic but, if executed well, could be more cost-effective than old-school comms.
In summary then, Cameron needs to be seen to have cut spend on bureaucracy and 'costly spin doctors'. At the same time he needs to communicate a single, positive vision for where his Government is taking British society. This will require bravery and the highest level of talent.