Doesn’t it seem odd that the curse was broken when true love’s kiss was shared between two non-Storybrooke people? Emma was FTL-born, so she gets that credit, but Henry was modern-day born, and in Phoenix! Then again, maybe Henry’s father was also FTL-born (Baelfire?).
The reason that Emma’s true love kiss broke the curse, at least partially, is because her parents’ hairs were used to create the true love potion, a drop of which was put on the parchment of paper the curse was written on. That is why she is the only one who could break the curse. That was how Rumpelstitskin designed the curse. He said as much to her in the finale when she came into his shop as a true believer. Emma was the key to breaking the curse, and Henry was the cause of her belief. The combination of the two was bound to have a powerful effect.
"That’s how you know you’ve really got a home. When you leave it, there’s this feeling that you can’t shake. You just miss it." Neal Cassidy