> How much does LibreOffice do that Word 5.0 doesn't, really?

It has to support and parse a billion more formats. Including the fact that MS word file formats are in some cases literal dumps from word's memory (iirc).

Rendering things properly is also a difficult problem to solve. Look how difficult it has been for much of the 21st century, to get a webpage uniform across all major browsers, and then realised that you not only have to display the same across all major browsers, but also be 30 years backwards compatible.