I know - and capping also loses in the crucial midnight-to-0430 window,
too, and there are probably other issues which don't leap immediately to
mind. That's why i qualified 'need' with 'really' - these aren't huge
issues, although i admit that the NR issue is pretty big.

Capping is supposed to work from 0430 to 0430. Also, with the new
fares, you get a 50p discount if you choose to sacrifice National
Rail, although that could be argued to undermine the integrated manner
of the One Day Travelcard.

Yes it does. In fact on the statement you get from Oyster detailing all
transactions for the last 3 months 1am is 25:00 and 2.15am is 26:15.
i.e. part of the previous day.