The emission rate of most crypto-currencies is actually relatively high, the problem is that their value have been increasing faster than the coin supply have inflated. To keep value stable, you need an intelligent entity which can control emission, which kind of kills the point of decentralization. Bitcoin halves it's emission rate every 210000 Blocks, or roughly every 4 years. This is because of an adherence to the Austrian School of economic thought. Ethereum is planning to move towards an emission rate somewhere in the realm of 0 < Grow Rate <= World GDP Growth Rate, which should make it's value increase slightly.

So to answer your question succinctly; The deflationary nature of Bitcoin is intended. It's quite possible to build inflationary Crypto-Currencies, but it would be difficult to gain traction with early adopters.