I'm sure we can do better; we just haven't tested the newer alternatives over a long enough time span to be sure. Take a look, for example, at the Long Now Foundation's Rosetta disk:
They made a disk of sturdy, corrosion-resistant metal, micro-etched thousands of pages of text on one side, and covered the other side with a design of words spiraling into the center and getting smaller, until they were no longer visible with the naked eye -- meant to suggest at a glance what the disk was, and how to read it. The text is a record of thousands of existing languages, like a modern, souped-up version of the original Rosetta stone.
http://blog.longnow.org/02008/08/20/very-long-term-backup/
They made a disk of sturdy, corrosion-resistant metal, micro-etched thousands of pages of text on one side, and covered the other side with a design of words spiraling into the center and getting smaller, until they were no longer visible with the naked eye -- meant to suggest at a glance what the disk was, and how to read it. The text is a record of thousands of existing languages, like a modern, souped-up version of the original Rosetta stone.
Clay tablets have nothing on that.