Why? Maybe there's something I'm missing. I thought it was kind of a close call to maybe try to get three seats together in the 4 seat middle section so we could sit on either side of him. Especially if we didn't have the car seat I might lean that way, so he can stretch out over two seats and sleep.

Another option might be to roll the dice, book only two adult seats, saving the $700 I'm paying for the child, and then book two aisle seats in the 4 configuration and hope the middle seats remain empty and we get all four seats. That's not a risk I'm willing to take though, drawing a full flight and having to hold him in our laps for 12 hours would be hellish, he's way too big and squirmy for that.