[bilog]

The intuition with the columns of pennies over a plate doesn't translate because in the plate case the surface is fixed (the surface of the plate) so the pressure depends on how much weight you put on it. In the case of multiple columns of water, the pressure you're looking at is the pressure on the combined surface of both columns, which remains constant because both the weight AND the surface are increasing proportionally, keeping the ratio (that gives you the pressure) constant.