if anyone has been cheated then it is the government (ultimately taxpayer) Taxation rates have been set based on emissions, and VW / Audi/Skoda etc owners have been paying too little tax for the poison their cars have been kicking out, so those owners have got away with paying less, so how they can now say they have been ripped off is beyond me.
A lot probably chose these cars as company vehicles based on a tax incentive basis, they have been running round in better performing vehicles than a real emission reduction would have been able to produce, and paying less tax for it.
Now if they had been told 'ok your real emissions take you up a couple of tax bands and you now owe us ££££'s' then that is a reason to feel aggrieved.
I am surprised the government is not after the lost revenue and making the owners pay extra.
I have been on the sharp end of a proper emissions reduction, where Fiat reduced the emissions by software so much that our (then new) Fiat 500 had difficulty pulling off and going up hills. That was a software modification in place all the time, not just for a test.
After Watchdog got involved Fiat recalled them, They re-flashed (remapped) the software and it was a different car afterwards.
Maybe that is what will happen to the VW's when they go for the modification, and they get down graded to perform to the tax rates they have been aligned with.
Now that would be reason for compensation.