<ul>
  <li>There are <$count filter="[tag[Contact]]"/> people in this wiki.</li>
  <li>There are <$count filter="[tag[Meeting]links[]!tag[Contact]]"/> non-contact tiddlers linked from meetings.</li>
  <$set name="totalTiddlers" value={{{ [!is[system]count[]] }}}>
    <li><$text text={{{ [tag[Contact]count[]divide<totalTiddlers>multiply[100]precision[3]] }}}/>% of all non-system tiddlers in the wiki are contacts.</li>
  </$set>
</ul>

As you can see, the percentage calculation cannot be replaced since count[] is not the final filter step.