Another Vernor Vinge concept I love is the "software midden heap", layers of software standing on the shoulders of and papering over the bugs of earlier software. Will anyone be able to excise rotting middle layers without breaking software compatibility?

For example, Vinge's A DEEPNESS IN THE SKY describes a software system thousands of years in the future that still uses the time_t epoch (and none of the system's space-faring users know the significance of 01970-01-01).