I may be wrong in my reading (I'm not English specialist...)...
but "More than 70 Filipinos and foreigners" do not mean 70 only but ... more... we do not have the precise number,
"arrested for faking documents" means they were doing, manufacturing, printing fake documents. So they were doing business with it.
So it's not only 70 people on 40000, we do not know the ratio. These 70 are not trying to immigrate, they earn too much money with this business...
So sorry I'm not sad for them... they deserve to be arrested. But I'm very sad for the dozens or hundreds of Filipino citizens who bought (at high price) these countrefeight documents and so were denied (all these are not arrested...) in any Embassy in Manila (and not only at the UK one). Every week you have people arrested at NAIA trying to travel with fake documents. If there are more than usual, then you have some words in a newspaper.
In Schengen countries POE, in the jetway at the aircraft exit, immigration officers are checking carefully the passports and visas with a special tool to check all the security signs put on genuine visas and passports. If the documents seems fake they bring the person to their offices where these undergo a full detailed documentation check in the immigration office. A second close check is done at the immigration booth. The shared visa database between Schengen countries ease the process. If they can't state quickly, the person is detained in the immigration jail (still in international area) until they get official infos on their documents.
For example at French Embassy in Manila, even if you arrive with NSO Sepca documents with the Red Ribbon (as requested), they systematically undergo an investigation with the relevant Philippines administrations to verify if they are genuine. And sometimes, but more often than we may think, the US Embassy send a person from the Embassy with private investigators at the place were the person who requested a visa live to check the infos given for the visa request.