Getting the entire index of nodes from REST API
The index actually sends 20 results per page. I highly recommend you check out the ServicesResourceNodeTests.test file in the services module for a better explaination but basically you can pass the page number you want to get each page of results.

The test file shows how it checks to see if the next page is empty:

// The n+1 page should be empty.
    $responseArray = $this-&gt;servicesGet($this-&gt;endpoint-&gt;path . '/node', array('page' =&gt; $page_count + 1));
    $this-&gt;assertEqual(count($responseArray['body']), 0, t('The n+1 page is empty'));


Another (my preferred) option would be to use the Services Views module instead and that way you can get all the nodes in whatever format you wish!