I'm sure plenty of either have happened - the block flexes letting the crank flex letting it break, or the crank flexes putting extra stress on the webbing/cap and they break. Given the successes with girdles I think that the block is more of a limit than the stock rolled fillet crank, but step up to a billet or forged crank (with girdle) or step down to a non-rolled fillet crank (without girdle) and I don't know. A typical machine shop bill to clean, check, prep, and assemble a shortblock (including new pistons and bearings) is $2000-$3000 depending on where you are, what pistons you use, and exactly what machining is done - spending $200 more for a rolled fillet crank adds 10% or less which sure seems like cheap insurance to most of us.