One potential problem with certain types of fruits is that they need to cross-polinate with other plants to produce fruit (this is particularly true with melons and cucumbers). If you have a number of plants that started from seeds that were in the same fruit, you could end up with deformed fruit. It's kind of like children from an incestuous relationship have a high likelihood of being born with birth defects. Seeds in packages come from different fruit. So, it's nearly impossible that you would have two plants from seed from the same fruit.
Another thing to consider is some seeds will not sprout until they have had a chance to dry out first. Although, if you've ever grown tomatoes and a rotten one falls to the ground, you will have dozens of tomato seedlings sprouting up from that location the next year. But, for lots of different types of fruits, the seeds have to dry out and there's something about getting them wet again that spurs germination.
Also, consider that packaged seeds are from fruit/veggies that are from a top-quality stock and only the best seeds are harvested. So, there's more likelihood that you'll have bigger, better plants that will produce bigger, better fruit.