dumb quest: why PIR example shows pull-up (P8_19) to 5v when GPIO pins are 3.3v tolerant?

http://beagleboard.org/Support/BoneScript/PIRMotionSensor

From
https://www.sparkfun.com/products/8630

This unit works great from 5 to 12V (datasheet shows 12V). You can also install a jumper wire past the 5V regulator on board to make this unit work at 3.3V. Sensor uses 1.6mA@3.3V.