Policy these days is to minimise the number of buses that stop short of the terminus. This is one reason why so many routes have been split (like the 63 / 363). It makes for clarity amongst users.
Yet TfL in their wise wisdom decided to extend the P12 to Brockley Rise instead of it's old loop route round the Nunhead area to Peckham which has made the route more unreliable.
Now imagine what would happen to the 63 especially during the peaks when Honor Oak Park is full of traffic, in the time it'd take a passenger to reach the station from the Wood Vale end of Forest Hill Road, they might as well walk.
In any case, the 63/363 offers an excellent service to Peckham Rye station, which will eventually be on the ELL in late 2012.