Let's compare the ISS to a car, for a moment.
Think about your 20 year old vehicle and the shape it's in. It's got, what? 150,000 miles on it? It's starting to rust out, the trunk leaks when it rains, the radio only works out of 2 speakers, the air conditioner works great in the winter time, the right-front door won't lock and the left-rear window won't roll down any more. Not to mention the big ole dent in the front fender where you misjudged a turn coming out of that parking ramp...
Now, compare it to the ISS. by 2016 it'll be 18 years old, and have traveled approximately 2.7 BILLION MILES! What would your old beater look like after 2,700,000,000 miles?????