The obligation to tell the public about any change in the target effectively means that monetary policy can not be used for political ends, because monetary policy achieves short-term increases in economic activity largely by producing surprise inflation.
It is hard to see what political gain would be achieved by a government which announced, in an election year, that the inflation target was to be increased to, say, 5 to 8 per cent. The effect on interest rates and the exchange rate would not be conducive to winning votes!