Drives in a RAID array don't have any shorter a lifespan than a drive on it's own. As long as the RAID array is used in the same manner as the single drive would be. It's not fair to compare a RAID array used in enterprise computing to a single drive used at the consumer level. Actually using drives in a RAID 0 array could actually extend the lifespan as the write wearing would be shared across the two drives. A single drive would end up with twice as many writes as a single drive in the array would.
So to answer the last part of your question, when a drive fails in a RAID array, it was destined to fail regardless. Had it been a single drive used in the same environment, it would have died either way.