SingleThreadModel

If a servlet implements the SingleThreadModel interface, then the servlet container may create multiple instances of the servlet so as to handle heavy request load. Here, all request will still be serialized to a single instance only.

This is event true for a distibutable application. I mean that if the application is distributable and its servlets implement SingleThreadModel interface then also the above described behaviour may happen internaly. The only difference will be that there will be multiple instances of servlet per VM.
Note: Multiple VM's run on each machines in case of distributable application.