why are these exhaust capped?

[resque2]

I saw many modified cars have their exhaust closed like this. Why?

[homer]

since the mufflers are pointing up in the sky, if they don't cap them, when it rains, water is going to get into the engine.. and that's a mess.

looking at the so wide-tire, i guess the rider is learning how to ride a motobike since he's afraid of falling over.

i have never seen a modified car with muffler capped. Cars' mufflers are usually underneath the car, i think there is no need to cap. On a truck, things are different since the exhaust pipe is pointing up, that's why you sometimes see the tips are bent to point horizontally. If not, there are hinge-caps at the top close the pipe when the engine is not pushing out smoke.