I think hubscore reflects both having done good work (writing pages) and over-all use of the website.
Having well written hub pages does the most insofar as giving one a high hub score. But also using the entire site influences score.
For instance, answering a few questions here and there will absolutely raise your personal score. Doing some forum interaction raises score a bit. As does commenting other hub pages, and (this raises score more than the others - in my non scientific opinion) doing the hub-hopping raises score.
A few years ago I got up to a 99 score, for about a day (ha!) I've never seen 100, and don't expect I will. To be perfectly honest about it, the score into the 90s is all I need, as I'm really here to see how much money I can make by writing about things I care about.