It is actually possible for a government to offer a savings vehicle that preserved purchasing power, by just debasing it as fast as or slower than productivity growth. This would split the increased purchasing power between the government/corporate fiat system and the individual saver, typically in favor of the government and its cronies with some left for the saver. The fiat system doesn't have this much restraint however, aside from the approval of your typical broad indices like S&P 500. Additionally, most people still fall for the illusion of money and don't examine how they are either barely keeping up with the price level or getting obliterated by it.