How long should a cartridge last?

I have a Shelter 501 that started acting up (skipping...I also didn't set my new arm up properly). The folks at The Analog Room said I needed a new cartridge, which I just got. So, my first Shelter lasted about 3 and a half years and saw very regular use, perhaps an hour a day, maybe more (on average). Still, I was surprised it went kaput so fast. Do folks typically just buy a new cartridge (as my dealer recommended) or just get a new stylus? I did not quite understand the explanation...the "suspension when out"...I could call my dealer and ask again, but I thought I would post here and see what other folks might say.