Measuring tailpipe emissions is not cost effective.
A visual inspection and obd scan IS, and it is the "hard line" the EPA drew, and enforcable.
And remember, the tuners who got into trouble were turning emission shit off. That is what drew attention, not fine tuning fuel and spark. SCT stayed in business by making the person editing the calibration sign an agreement not to disable or bypass emission componenets. The PRP software still has full access to the tune, nothing was disabled in the software.
Seems pretty straight forward to me. Play by the rules, and modding is ok. Yet there are those who just dont get it or give a fuck about the laws. " Must Remove Emission Parts at all cost........that is selfish.