The additive only last so long and has to be topped up.
Cars with ad blue have a seprate flipper cap for it. You just keep topping it up like screenwash. Quoted cost earlier was £50 a year.
The reason this wasn't fitted as standard and why VW cheated was purely down to cost. VW finance dept calculated it would cost 300 euro per engine to fit this extra hardware so they decided not to bother and just to use the ECU software to cheat the tests.
The way they cheated was by running the car in a low emission low power mode when it was being tested. it then switched all that off and ran at full power when back on the road. The cars implicated in the test cycle didn't have ad blue.
1) VW goes to sell Dielse in europe
2) VW finds out in order to pass tests they need to fit 00 euros worth of extra hardware to pass the 2.5x more stringent US tests. This extra hardware is fitted on some other new VW diesels and is called "Ad Blue".
3) VW says this 300 euro per model extra expense isn't worth it, ships the car with ECU software to cheat the tests, and without ad blue
4) VW gets found out.
5) VW has to pay 300 euro per car to fit the ad blue system after all , plus many many many ££££$$$ i fines.
The reason the cars ran in the cheat mode only during the tests, is likely because power or torque or similar was reduced to in turn reduce the emissions.
Unless it turns out these cars had a urea system fitted all along, but only used it during the test cycle, and the only change is now you have to fill up the system as it runs out ? But that's not what I've read so far. Happy to be corrected.
But why bother fitting the system if the whole reason for the cheat devices was to save the 300 euro per engine VW calculated it would cost ?