Its not that the needle roller bearing is fragile, but the location. The environment inside the bell housing is subject to the dust from the clutch plate, water, oil grit/dirt etc. that causes this type of bearing to fail, some engines do use ball bearings but they are sealed so all the crap cant get in and damage it.
The roller bearings inside the T5 or any other G/Box are swimming in oil, and the inside of the box is generally quite clean.
Also the bearing is only needed when in gear and the clutch depressed, (example when the car is stopped and in first gear) other wise the bearing does nothing as the crank shaft/flywheel and the clutch plate/input shaft are solidly connected when the clutch peddle is released.