The dificulty comes from the release clause, and the 'final amount' including a currency conversation from Euros, the additional fees involved in the transfer, and the cut which goes to Ajax (?). So whilst it is being reported as £70m+, the final value is probably somewhere in the 60s. Still a great deal of money.
It probably helps Liverpool to allow the number to be reported as lower, as it does Barcelona. Barca can say they have got a bargain, and Liverpool can say they don't have as much money as expected to other clubs as they attempt to sign players to replace him. The only negative is the fans consider it 'less than what he's worth', but frankly that matters little if this lets quality talent come in to replace him.