Reading over TRULY UNDERSTANDING VIEWSTATE the author suggests:
When ASP.NET parses the form, and finds a tag with runat=server, it creates an instance of the specified control. The variable name it assigns the instance to is based on the ID you assigned it (by the way, many don't realize that you don't have to give a control an ID at all, ASP.NET will use an automatically generated ID. Not specifying an ID has advantages, but that is a different subject).
What advantages could one gain by not specifying control IDs? My quick searching didn't turn anything up. Thanks for the help.