Sometimes it comes down to the old adage, you get what you pay for. My Shimano 105 group is 15 years old and the only thing I have replaced is the chain. My Campy group is 16 years old and is still original. Once a year all the bearings get cleaned and greased. Average weekly mileage is about 50 on each bike except in winter. Wear and tear on tires, tubes and brake pads is normal. I buy tubes four at a time. I don't even patch tubes anymore, just replace. Good quality bicycles will always reward you beyond their ordinary equivalent.