Pink Oyster Readers

http://www.tfl.gov.uk/corporate/media/newscentre/12483.aspx

TfL has introduced pink coloured Oyster readers at Gospel Oak, Gunnersbury, Highbury & Islington, Kensington Olympia, Rayners Lane, Stratford, West Brompton, Willesden Junction and Blackhorse Road.

"The introduction of Oyster route validators will mean that the Oyster system will identify when passengers have avoided travelling through Zone 1 for those journeys where there are several different choices of route."

I'm confused because I assumed swiping on the platform reader at Stratford told the system you'd changed at Stratford. Is the only change the colour? Also, if you travelled Barking to Blackhorse Road via zone 1, you would take much longer than the direct route, so Oyster ought to be able to work it out by time. Furthermore, the readers between the Gospel Oak Line and tube at BHR were taken out of service when Oyster PAYG was introduced on the B and GO line.