Note that the clientInformation reference is another name for the navigator object. We could be uncharitable and suggest that this is an attempt by Microsoft to avoid publicising a competitor's browser name in any scripts that they publish. It is likely that scripts written by and for Microsoft products would use this syntax rather than the navigator property. Therefore it follows that they will break on Netscape Navigator.
It is possible that future versions of Netscape Navigator and other browsers may support this property as a means to ensure they can continue to provide cross browser feature parity with one another. It is not supported in Netscape 6.