It has been said that the creation of new ETH will be discontinued with Caspar and PoS. Is there a fundamental reason why this is necessary, rooted in the protocol or is this a deliberate decision by the Ethereum Foundation?
The creation of Ether is a subsidy to cover the costs associated with proof of work. Since Casper and/or proof of stake will no longer incur these costs, all computing resources of miners can be focused on transaction processing, which they get paid for. No reason to double pay miners.
After PoS switch at about the 90 Million total issuance mark, Vitalik expects an inflation of a fixed 0-2MM per year. The details are being ironed out with Vlad still. That is less than 2% per year and a disinflationary currency as it is relative to total supply.