Unlike paper money where the lowest you could go is 1 cent in most currencies, it's technically easy to divide an Ethereum coin (or other coins) into smaller units, like 0.00001 ETH, so the total number of coins in the world is not a big deal : if the demand is high, the value of each individual coin can go up, and you use divisions of a coin to pay for things.
Also, unlike Bitcoin, coins like Ethereum produce new blocks more often (for example 3 ETH reward for every block created, which is every ~15 seconds) and this amount of reward can be adjusted by developers but only if more than 51% of the miners agree to upgrade their software to follow the new "set of rules" of the coin.
In the case of Ethereum for example, this happened last year, in October ... they decreased the difficulty to make mining easier, but lowered the reward to half the amount in return, you can see the chart here :
https://www.etherchain.org/charts/difficultyThe point is, if there's a need to increase the number of coins to "keep up with economy", miners will vote and if more than 51% agree, then amount can be changed.
Bitcoin suffers from the long block times (10m), small number of transactions per block (~2 transactions per second I think), high transaction fees, and the Chinese miners don't want to do anything that would lower their profitability. So they basically dug their own grave... the bitcoin is becoming less and less attractive.
In comparison, Ethereum runs around Bitcoin and they have active team of developers who are working on improving things substantially, like working on having proof of stake and proof of work systems simultaneously (mine some blocks, validate some blocks without mining) and they're also working on sharding, which will raise the number of transactions the coin can handle exponentially.