Yeah, but weigh up the chances of that (most people don't get kidney failure in their life) versus the extra opportunities that you get from the money. If you're dirt poor in China, $3400 might be just what you need to get yourself started in life and catapult yourself up into the middle class.
Buying an iPad still seems like dubious value, but... hopefully he did something better with the rest of it. And I guess if you don't have any other computer then an iPad just might be worth 20% of one of your kidneys if you can use it to educate yourself or start a business.
But if I were dirt poor in China, and I really did think that $3400 would be enough to give me the kick start to lift myself permanently out of poverty, I'd do it.
I suppose the real problem is that there's some minimum rational price for which it's sensible to sell a kidney... and a bunch of irrational people who are willing to sell their kidneys for less than that. So none of the rational people will ever get a look in, and a legalised kidney trade would only lead to misery rather than good deals.