4 Bolt Main

Does anyone know why some engines with a 4 bolt main will only have a 2 bolt cap on one end of the block?

The bearings in between the ends take the load of multiple pistons/rods(on both sides of the bearing) while the ones on the end take less load because there is only a load on one side of the bearing.

I believe it also has to do with if the engine uses one piece or two pieces seals- not possative though.

Alright, that makes sense guys, thanks. It just confused me when even a Keith Black top fuel hemi block (up to 8000 hp) used 6 bolt mains on a y block design yet the end was still only 2 bolt.