They don't need to state the will because when you have bitcoin you have also your wallet. And if the owner of that wallet died and he wants it to give it to someone or love ones he just only need to give the access of his/her wallet to person that will receive that wallet.
Yes.I agree with you.Bitcoin is as like a profit.If you want your generation to enjoy the holding bitcoin,just share the knowledge of wallet to your son or daughter.If you not share that means,it will became useless after your death.You are investing the life savings money,so you should take care of your wallet.Don't waste it.