It is because his arrest is seen as demonstrating that the unseen protection from certain politicians which, it is believed, enabled him to remain free for 24 years and allowed the Mafia to flourish, has collapsed. It seems to mean that the prosecutors, the police and the carabinieri are at last no longer fighting with their hands tied behind their backs.
'This is a historic turning point,' said Luciano Violante, chairman of the parliament's Anti-Mafia Commission, which had begun investigating the links between the Mafia and politicians revealed in part by pentiti (supergrasses), some of them close associates of Mr Riina. 'Now we can fight and beat the Mafia,' he said.
Quite how it all worked and who was involved is unclear. But the commission has learned that Salvatore Lima, a Christian Democrat and the most powerful politician in Sicily, was the Mafia's chief link with the rulers in Rome, arranging favours, protection and judicial leniency. He was killed, they said, after he could no longer produce what was wanted.
Here, at least one pentiti has mentioned the name of Giulio Andreotti, the powerful leader of Lima's corrente or faction within the Christian Democrat Party and a former prime minister. Mr Andreotti's assurances that he had no idea that Lima was involved with the Mafia and still does not believe it, convinced few.
Toto Riina, as he is called in Sicily, has partly himself to blame for losing this protection. The Mafia had been a shadowy parallel power, getting what it wanted through favours or threats, sometimes feuding bloodily but largely anxious to ensure it could carry on racketeering in peace. Mr Riina instigated a head-on conflict with the state - and lost.
The more people he murdered - particularly courageous, dedicated men such as the magistrates Giovanni Falcone and Paolo Borsellino - the more the public was outraged and the authorities were forced to crack down.
He also paid for changing the Mafia itself. From a loose association of clans with one accepted 'Boss of Bosses', he turned it into a dictatorship of fear, eliminating anyone, even his closest friends, who stood in the way of total control for himself, backed by his Corleone gang. And slowly he started to throw out, or wipe out, the old Mafia figures and replace them with new people organised in different ways so that everything the authorities knew about the Mafia would be useless.
But this policy produced the pentiti, sidelined, embittered and disgusted, who accepted the protection given by Italy's new supergrass law and told all they knew - 270 of them to date.
No one knows yet what led to Mr Riina's capture and whether he was betrayed. But the Interior Minister said there were rumours of fierce disputes in the top Mafia echelons about his policies.
The battle with the Mafia, experts warn, is far from over; but the reign of terror Sicily has known under Mr Riina in recent years, almost certainly is.