If you were using the default AddThis configuration it's using what we call Preferred Services. These are different for each individual based on their past sharing history and what services are most popular in our service. This is designed to make it easy for users to share to their preferred service and to increase sharing. If you want to specify which services are displayed, instead of using these buttons:
<a class="addthis_button_preferred_1"></a>
<a class="addthis_button_preferred_2"></a>
<a class="addthis_button_preferred_3"></a>
Replace the 'preferred_#' with a service code, like this:
<a class="addthis_button_facebook"></a>
<a class="addthis_button_twitter"></a>
<a class="addthis_button_email"></a>
A full list of service codes is available here:
http://www.addthis.com/services/list