I can count on the fingers of one hand the number of times I have had my ticket check on the train between Stevenage and KGX, STP and LBG (and vv) since ticket gates were introduced. It wasn't even that common prior to this.
I assume the assumption is that if the ticket gates are in operation, this effectively does the Revenue Protection Officers' job for them. Often, their mobiles can't read the Key Smartcards they have been issuing, which, frustratingly, are only valid to Foxton and Huntingdon northbound in any case.
To be fair, I have seen even less revenue protection in rural Germany than in the UK. The ticket machines there often don't sell the tickets required, or will only accept cash, and often only coins, and very, very rarely, cards (and if they do it will almost always only be German Giropay cards). So DB only have themselves to blame for faredodging at epic levels. I just had a wonderful weekend in Luxembourg, where, of course, 2nd class transport on trains, buses, trams, and funicular is free, and buses that much quicker as people aren't haggling over the fare.