Assuming your 4runner was petrol not diesel? If so that is why. Diesel being based on compression rather than ignition doesn't give as much engine braking effect, when the piston goes up and squeezes the air in the cylinder, the compressed air acts like a spring and pushes the piston back down even though no fuel was injected and so no bang... On big trucks they have a j-brake which they can engage, essentially it allows a valve to open at the top of the stroke, releasing the trapped air, then closing again, so the down stroke isn't assisted by any compressed air and is actually pulling a vacuum helping brake further...I agree with Jose. Also depends on whether you're driving in a heavy urban environment or more highway driving. And simple things, like always following too close, will help increase brake wear (more panic stops and/or left foot braking/riding the brakes). 25,000 miles doesn't sound too bad.
I finally picked up my Q5 TDI last week. I've been taking it easy so far (still breaking things in), but have found that even in sport mode I don't get much engine braking effect (compared to my old V8 4Runner with a 5 speed auto). Just wondering if others find the same thing or maybe I should be going after those lower gears a bit more aggressively.