Bitcoin is inflationary as well, till all coins are mined....or am i missing sth.?
It isn't inflationary since the same number of coins is set to be issued regardless of the total amount in circulation, an inflationary model would imply that 4% of the current number of coins in circulation would be issued over the next year.
I thought inflation was just any increase in coin supply. Bitcoin is technically supposed to be neither inflationary nor deflationary once fully mined but will be very slightly deflationary in practice because it is inevitable that every year, some people will lose their coins.
The problem with inflationary models is you effectively issue new coins to reward people who are working on the network, the number of coins is determined by the number of coins in circulations (a.k.a 5%/10%/3%) thus demand needs to expand accordingly. Ask yourself what would happen if everyone on the planet adopted such a coin and there were no new people so there is zero demand but new coins are still being issued? And most importantly why would anyone expose himself to additional risk?
Advocates of inflation claim that it discourages hoarding and speculators (e.g. why would I buy a car today if my money will be worth a lot more the next year?) as well as a more stable price. All of the cons of inflationary systems outweigh the pros by a whole lot, this is why inflationary currencies crash constantly while gold is still strong thousands of years down the road.
Prices would simply rise in proportion to the inflation rate assuming zero population change and identical demand (these assumptions are pretty unrealistic when it comes to cryptos though). If you had 100 coins and 100 people last year and 101 coins and the same 100 people this year (i.e. you introduced 1 coin into the system) and demand for the coin stayed the same, then each person would now have an extra 1 percent added to their balance. A coin would be worth 1 percent less so nothing would be lost and their net worth (as measured in coins) would stay the same, and something that cost 1 coin this year would then cost 1.01 coins next year.
After many years, your hamburger bought using coins could be worth twice as much coins, but it wouldn't be an issue if you earned twice as much coins due to inflation during that same time.
As you might have already guessed, the coin that I am thinking of is Peercoin. Peercoin doesn't discourage hoarding. In fact, it does the exact opposite. It promotes hoarding because only those who hoard their coins and thus support the network would benefit from the proof-of-stake minting.
I disagree with incorporating inflation into Bitcoin however and I think it would be a stupid idea to change Bitcoin's protocol just to please the existing inflationary system, but as a fan of Peercoin which uses an inflationary model, I do also think that inflationary currencies can work.
Note: Also, to keep things simple, I'm ignoring the contribution of transaction fees here.
Edit: Some minor rewording.