Big blocks have a tendency to "fret" the caps, which means the caps "bounce". Has nothing to do with bending of the block. Its all about clamping force. When the caps bounce the webs take the brunt, because the crank IS hammering the caps and webs. Attempting to "lock down" the caps with a girdle, forces the webs to take ALL the pounding and they simply are not strong enough in a stock block.

The pic you showed, from a small block, could be a number of things. Maybe the main housing bores are not perfect. The caps could be moving and "egg" shaping the hole, which would result in what you are showing. Could be crank flex. A big block usually shows bearing wear at 6 and 12 oclock on the bearing, when you are hammering the caps and fretting them..............At least the SEVERAL I broke looked that way. And the fretting is not always caused by something being wrong, as in tune or rpm. Sometimes it is simply POWER and more of it than the general design can hold

Monte