The blockchain is not what's responsible for all of the things you describe; rather, it's the dominant algorithm for psuedo-randomly distributing the ability to modify the block chain, called proof-of-work (namely Satoshi's version). There are other, just as computationally wasteful algos that try to be memory hard as opposed to cpu-hard (Cuckoo cycle PoW for example.

Lots of folks are working on different, less wasteful ways of making blockchains more resistant to attack - the most well-known of the alternatives being proof-of-stake which is essentially a betting scheme. It's a fascinating area of computing if you go beyond the hype over the BTC price.