there is discussion on the Arduino dev list about resolving this problem so at some point in the future these includes won't be necessary.

Author: nicolaspanel

examples/SimpleEncoderFirmata/SimpleEncoderFirmata.ino

@@ -112,8 +112,10 @@
  *--------------------
  */
 
+//* Due to arduino issue, Wire and Servo libraries need to be included. Should be fixed in later versions
 #include <Wire.h>
 #include <Servo.h>
+//*/
 #include <Firmata.h>
 #include <utility/FirmataExt.h>
 #include <utility/FirmataReporting.h>