me neither, but playing devil's advocate. i think it was brad roberts who made the statement. some ecus do use feedback from the second set of o2 sensors to refine the data from the first set, and i think the bosch units in our cars have that ability. whether they do or not is questionable. and if they did, realise that deleting the second set wouldn't result in big changes in afr, but rather slight changes, perhaps more erratic short-term trims, etc. here's a link:
https://mechanics.stackexchange.com/questions/37442/is-the-after-catalyst-oxygen-sensor-used-for-engine-mixture-control
and here is info regarding how the o2 sensor accesses reference air via the wire sheath:
http://www.autotap.com/techlibrary/understanding_oxygen_sensors.asp
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