Mate
It comes down to unrefuelled range.
Buccaneer approx 2,300nm
Vulcan approx 4,750nm
Put bluntly, the Vulcan could miss more refuel brackets than the Bucc and get home...
I hope this helps...
LJ
PS They could have put pavespike on the pylons of the Vulcan, but I guess they didn't fancy hanging about lasing the target. Drop 21 bombs and knob off in quick order was the tactic used (shame only 1 in 21 hit the runway though!).