Hello Devon, joq

The reasons cited for the turtle reference are;

1.  Reference to the first mobile robots made; William Grey Walter's Elmer and Elsie - Turtle robots
2. LOGO Turtle, probably the simplest GUI based simulations for navigation. ROS also has a package very similar to the LOGO Turtle and it is often recommended as a tutorial for newbies.
3. "It's turtles all the way down" - iconic references in various popular texts, viz. Brief History Of Time
   
4. Proverbial reference of the turtle and the hare - where hard and consistent labour wins over street smartness - isn't ROS much like that
   

So, seems we are stuck with the turtle, least for some time to come ! :-)

Regards,

Arkapravo