Darkcoin has done something really impressive by making a coin distribution strategy that no other cryptocurrency can claim to have implemented.  It ultimately does have a limited supply. New coin generation (and inflation) will gradually taper off over time at a stable rate of 7% annually. Compare this to the much sharper 50% drops every 4 years in bitcoin.

Additionally, the darkcoin block reward still adjusts on a block-to-block basis due to difficulty.  Maximum:25, minimum 5.  If the network hashpower is too low, the payout increases as an incentive.  In the long term, it is incredibly likely that added network power will simply reduce the reward rate to 5 DRK per block.  This results in the projected total number of coins reaching approximately 22 million over the time frame shown - slightly more or less depending on how quickly hash power is added.