OK, here's another one then: http://dominion.isotropic.org/gamelog/201108/22/game-20110822-171917-4a9037cb.html
Let's go through that one:
— guided's turn 1 —
Buy Chapel
— guided's turn 2 —
Nothing
— guided's turn 3 —
Draws C/C/C/C/E
Buys Bishop
— guided's turn 4 —
Draws Chapel/C/C/E/E
Trashes C/C/E/E
State of draw right before end of turn 4 draw: 1 Copper
State of discard pile before reshuffle: 4 Coppers, 1 Estate, 1 Chapel, 1 Bishop
Draw is 4 Coppers, 1 Estate, leaving a draw pile of 1 Copper, 1 Chapel, 1 Bishop -- Chapel and Bishop both miss the shuffle.
— guided's turn 5 —
Buys a Silver
State of draw pile: 1 Copper, 1 Chapel, 1 Bishop
State of discard pile before reshuffle: 4 Coppers, 1 Estate, 1 Silver.
Draw is Chapel, Bishop, Copper x3.
Left in draw pile after reshuffle: 2 Coppers, 1 Estate, 1 Silver
— guided's turn 6 —
Chapels Copper x3
State of draw pile: 2 Coppers, 1 Estate, 1 Silver
Discard pile: Chapel, Bishop
Draw is: 2 Coppers, 1 Estate, 1 Silver, 1 Bishop -- Chapel misses the shuffle again.
— guided's turn 7 —
Bishops an Estate, buys a Silver.
Draw pile is: 1 Chapel
Discard pile: 2 Coppers, 2 Silvers, Bishop
...and from there, play is predictable and deterministic, as you only need to trash one more Copper, which you're guaranteed to draw with a trasher. So, yeah, that was a case of the chapel missing two shuffles and the Bishop missing one shuffle -- it's admittedly a case where Chapel/Nothing sucks, but obviously there's a chance for either strategy to miss two shuffles.
Look man, weird pathological cases for Chapel/nothing aren't especially less common than weird pathological cases for Bishop/Chapel.
How do you know?
Missing turn 9 in both cases is very rare (assuming turn 3/4 Chapel). The thing that actually matters is weighing the chance of making turn 8 vs. the extra chance of dropping Chapel to turn 5 with Bishop/Chapel.
I agree that that's the more important issue.
If you're talking about playing one strategy against the other, you need to consider that Bishop/Chapel is likely up a VP chip in the case where both make turn 9, though of course playing one against the other there's the whole other issue of trashing on your opponent's turn that we haven't analyzed at all yet.
I think that in the case of a mirror strategy, Bishop/Chapel is the way to go. The extra shot at a trash on turn 3/4 probably significantly increases the odds of a turn 8 Province, and getting a turn 9 Province essentially is headed for a draw or a coin-flip based on who Bishoped the most Estates.