You seem to be missing a rather important point: none of the grayed out labels in the Yahoo registration form are actually examples. They are simply a compact way of presenting labels for (sub-)fields.

Using this UI behaviour for examples seems just about the worst possible use imaginable, since there is a high risk of confusing the example with an actual filled-in value. Plus, for more complicated/confusing fields, you can't actually type out your result with the example as a reference, because it disappears as soon as you focus the field.