Well the burning function needs to be coded into the blockchain on the protocal level so like Bitcoin doesn't have it but STEEM does, but steem will never have a fixed supply of tokens. The reason for the burning is because there aren't enough users competing, wanting, using, buying and selling steem and each day new steem comes on to the market it means more coins chasing fewer users, goods, services etc. In theory the more currency produced and the production remains the same the weaker the purchasing power. 

If we are to improve the purchasing power we'd need more users, more use cases and more ways to remove steem from circulation such as burning it for certain types of transactions or promotions for attention to your content or advertising