I just had my 25,000 mile service and the service tech asked if I just had the brakes done... Turns out I have about 90% of the lining left on the front and rear pads.

So I would say, not 5% remaining on the rear pads is not normal. Are both sides (left side and right side of the car) worn down the same? If so, that would make me suspect a problem with either the ABS or some sensor controlling the rear brakes. Usually if a caliper sticks, only the right or left set of pads is affected, and the pads on that side normally don't wear evenly when the caliper sticks.