When I went to re-program a robot I've been programming with the 1.5.5 R2 IDE, with the 1.5.6 R2 IDE, I noticed several missing libraries. Including, the SERVO library. But, they were still there..
Case in point: If you add any libraries, either in the \programs\arduino\libraries (as example, C:\programs(86)\arduino1.5.6\libraries), OR in User folder (Example: C:\users\gelfling\My Documents\arduino\libraries\ ) It will actually push something out of the list. (as an example, I recently added a SHT2x Humidity/Temperature chip library, to read temp/humidity where the robot was standing), the Files\examples\Servo examples were missing. (Yet, they did exist in the drive folder.) BUT.... the IDE refused to load servo.h, resulting in an Undefined error.
I've noticed this happens under BOTH Windows-7 & Linux (x64) versions of the IDE. It's as if there is no scroll-ability to the examples pull-down list (it stays solid to the height of the screen)
I've tried swapping the Servo library to the Sketchbook folder (user\???\My Documents\Arduino or root/home/????/arduino ), but they still won't show or load.)
So... It's either time to scour-out the old 1.5.5 R2 install file, or all the way back to the 1.0.5, which don't seem to have this problem.