Good point about a balanced DC supply with grounded neutral Jon. The op-amp is an excellent example.

There are plenty of other electronic applications of DC with positive and negative (with respect to ground) supplies of vastly different levels.

In high-power tube transmitters, for example, it's quite common to need a supply with a positive (B+) line of hundreds or even thousands of volts, while at the same time you need a supply which is negative with respect to ground (C-) of maybe 30 to 100V (used for grid bias).

In DC power systems there are also examples of some strange unbalanced-about-ground systems.

The London Underground (subway system), for example, has a 630V DC supply using a four-rail system (two running rails, plus two completely separate and isolated conductor rails). Apparently they have the supply arranged so that the outer rail is at about +420V to ground and the central rail at -210V.