I think nubcake's point is that the stock tune runs on the lean side, and with this, the EGT's can get up there under a long load pull that make the sensors tell the computer to add extra fuel. In this case, you need the sensors in tact so they work as they should to save the motor from running too lean in these situations. If you are not familiar with fueling, there is a fine balance of too little or too much fuel in which can be different in every running situation (starting, idle, cruise, hard pull, decelerations). Too much, and the car will run cooler, but will be sluggish and have less power...then there is a sweet spot in the middle with strong power and proper running....too little and the car will run lean and can get very hot which can cause damage.

With a custom tune from an amazing tuner here on the boards, , extra fuel can be added in the right situations so it doesn't run as lean as the stock tune. If you don't run too lean, then the EGT's will stay lower, thus making the sensors unnecessary as they'll never reach the thresholds to add that extra fuel. A custom tune isn't tricking the sensors, it's making the car run richer when needed so the EGT's aren't getting too hot to trip the sensors.

As far as I know, and others may correct me, the EGT sensors are more of a failsafe in an emergency situation (lean running on hard pulls for instance) and not used to control normal operations like a MAF, coolant temp, crank position, or O2 sensor does with constant input to the ECU. The car is happy to run without input from the EGT sensors if they are tuned out properly so the ECU isn't thinking that they are disconnected or not working correctly (achievable with a custom tune).

Hope this is helpful.

Again, I could be wrong with this assumption, but maybe the codes that you see are just saying that the EGT sensors were activated (but are not broken), showing that you did have a lean situation from time to time as nubcake says is common with the stock tune under hard pulls. My old car was a 2.7t A6, and the sensors were faulty...this put the car into limp mode that cut boost way back and added fuel...it was very obvious...the car ran fine, just no real power. I put some diodes in there to trick the ECU into thinking they were fine (I know, ghetto fix, but helped to identify the issue) and the car had full boost and power. Limp mode put it at about 5-6 psi on the boost instead of 16-20.