Tristán White wrote:

I've noticed, in the past few weeks, a decrease in courtesy when trains
actually wait for passengers to leave the arriving train across the
platform.

Sorry, that made no sense did it? I'm talking about things like Finchley
Road (Metropolitan to Jubilee) and Mile End (District to Central) and vice
versa.

(snip)

I must say though that the courtesy between DLR trains at Poplar (people
going from Canary Wharf to Beckton and changing at Poplar) is still alive
and well and trains indeed wait. But no such courtesy between District and
Central any more.

The courtesy you speak of at Poplar is courtesy of the computer! The
DLR timetable is specifically designed to enable cross-platform
interchange between two trains at Poplar - if you observe what happens
there you'll see that two trains very often pull into the two faces of
the island platforms (i.e. facing each other across the island
platform) at the same time - this is no accident!