They absolutely are in a daft place. I have had to ask before and the DLR agent conceded that they are not very well placed. I too went to the top of the escalator and realised I was in the DLR "sterile ticket zone"

To make matters worse (insider info from the DLR tea-break rooms) DLR train captains have revenue enforcement targets (something like 10 penalties per month) They don't much like having this target so actually endeavour to do it at LCY where the catch rates are higher because a) The machines are hidden and b) The trains are full of Johnny Foreigners that are mildly disorientated. Hitting their target at LCY is better than say at bank where regular travellers have period passes.

So not only are the oyster swipers stupidly placed at LCY, your chances of getting nabbed for it are also much higher.