Imagine if they got the wrong sperm AND egg; which is entirely possible since it was in-vitro. Using this theory, the clinic could be held 100% financially responsible for the child until age 18!
I won't discuss whether this is right or wrong. But let's assume the clinic is a business. When you run a business, you want to get paid for your cost, plus some profit, and if there is a risk that you make mistakes, you add the probability of a mistake times the cost of a mistake. if there's a one in thousand chance of a million dollar mistake, then the cost goes up by $1,000. If people don't want to pay the $1,000, then they can't get the goods.