Reading between the lines Dave, I Imagine that you do(or did!) offer a DPF delete service? and are not really 'sitting on the fence'. All of Peters comments are correct, you are not telling me that you did not know that removal of an emissions device is Illegal? of course it is.
The problem in this country is that we make the laws and legislation in an effort to improve the environment for future generations, but make an absulutely crap job of policing these laws. The latest DPF MOT check in its present state is doing little more than paying lip service to the problem, but it's a start.
If someone had big enough pockets to challenge GM over the EGR delete software position then I am sure that they would be guilty of breaking 'The law' as well, just as we are by knowingly modifying diesel engines to emit excessive levels of carcinogenic soot into the atmosphere.
A couple of years back I paid for all my staff to be trained and accredited for gas handling as the government mandated that R1234 had to be strictly controlled 'in an effort to improve the environment for future generations'., It was made 'illegal' to knowingly add gas to a system known to be empty. As you well know, allmost all cars that request AC service have little or no gas, yet Quick fit and the majority of the motor trade will still top up first without leak checks, knowing full well that there is no policing of our industry, so lets go for it and to hell with legislation.
I know I am pissing against the wind in trying to do things correctly and it will have cost me dearly but at least i know in my own infinitesimal way I am doing my bit for the environment even though the law is not (yet).

The Most Reverand

Ed Kaps