It's really one of those catch-22 situations - Apple can't contact the original owner to verify if that iPad really belongs to them and they're not just some criminal looking to change their $0 iPad into a $400 iPad on the stolen goods market. And they can't just take those documents because well, the family could come back again next week with another stolen iPad and do the same thing.
Nonsense. There's no need to make it literally impossible to unlock a stolen iPad (probably unattainable, and certainly liable to deprive legitimate owners of the use of their property) - you just need enough of a hurdle to make it unappealing to thieves. I'm sure that the value of a stolen iPad is much less than $400 - and equally that the value of a locked, stolen iPad is much more than $0 (just use a bit of sleight of hand to sell it to some mug and leg it - thieves don't generally do warranties).
A solicitor's letter (for US readers: Solicitor = Lawyer, and probably a notary public to boot) is easy to verify and should be more than sufficient to confirm the identity of the new and previous owner. No thief in their right mind is going to go through the risk and expense of obtaining a credible fake solicitor's letter for the value of a stolen iPad - and I'm sure that bent lawyers are even more expensive than real ones.
Requiring a legitimate owner to produce a court order is going to cost them more than the value of a legally acquired iPad.