Mind you that this is a decentralized system, so there is no such thing as a central planning committee or someone to hold an axe above the miners heads.
This is what I meant with my comment about mathematics: humans are out of the loop.
By central planners, I mean the people who design the incentive mechanisms in the beginning. This language is the convention in economics (actually maybe social planner is the more common term.)
Rules in the blockchain hold the axe over the miner's head.
The fact that a permanent difficulty target has to be set a priori is troublesome. You have to really trust Moore's law here. If chips improve faster than you expected, you could end up with more inflation than you intended. Even so there would be a credible cap on the inflation rate.
You could put breathing room in by setting a high difficulty growth target (I thought 50% per annum was high, since it implies a 125% increase in computational speed every two years). As I understand Moore's law it is a 100% increase in computational speed every two years.