For me, one of the most useful things I was expecting Oyster to offer was
the immediate purchase from home of a one day travelcard.

It seems that the system can't offer either of those aspects. You can't
immediately purchase anything from the website - it takes slightly less
time than a paper cheque would to clear before you get the goods. Secondly:
You can't actually buy one day travelcards!

Why can't the system let me use one day travelcards? These are pretty much
the only form of ticket I ever use. It could be quite easy. It could simply
modify the pre-pay paradigm to assess whether your day's worth of pre-pay
fits within or exceeds the cost of a one-day travelcard (off peak or peak,
depending on time of first use) and convert the day's usage to a travelcard
and thus plateau out at the point of charging for the maximum of the
relevant travelcard used for journeys actually taken.

As it is, helped by the insane methodology of bus charging, whereby if I
wanted to go from a to b, involving 20 changes of bus, I'd be up for 20 bus
fares (unlike the tube, which simply charges a fixed extortionate amount
for getting from expensive place a to equally expensive place b). With
pre-pay, it would be far too easy to rack up a day's worth of travelling
that far exceeds the equivalent cost of a Caxton-press printed papyrus
off-peak one day travelcard ticket of olde.
--
Ian Tindale