The reason why area shields will always cut blocks has to do with CPU load. Otherwise, any block that is uncut has to be checked every tick (20 times a second) to see if someone smashed the block that is there.
Ok, great explanation. (the whole story)
The block-cutting, can't it be saved into files? I don't know if that's doable (with HD-access times and file size) or not. I can, however, absolutely see the CPU usage problem.