Almost all Oyster fares remain the same except:
-- off-peak bus journeys (from £0.80 to £1.00)

OK, so that's an extra £1 a week for me then. I can't help wondering,
what's the reasoning behind abolishing off-peak fares on the busses?

Probably so there is a simple marketing message of £1 oyster or £2 cash. i.e
double the price. It is not as effective a message if there is an element of
complexity.