Why does the ringer stop working after 2 years of service?

I set the ringer for "sci-fi" sound and now the sound stop working. Took the iphone to a at&t store and the sales person said that this is a common ocurrence. she said that she had a iphone 4g and hers did the same thing like other customers she helped . she also advised me to take the iphone to a aplle store. My question is why doesn't apple fix the problem before coming out with a new product.