If I understand correctly, the distortion correction is automatic, without menu-driven user settings/controls. The lens tells the body what it is, and what distortion corrections are necessary at which focal lengths. The body encodes the required correction in RAW files and applies the correction to in-camera jpegs.
If you only shoot jpegs you won't see the corrections, since they're done automatically. If you shoot raw, you'll only see the before/after if you use a raw utility that will ignore the encoded corrections. Photoshop/Lightroom automatically apply the corrections to raw files using native Adobe raw utilities. There are some raw file utilities that will ignore the encoded corrections, and so allow before/after correction viewing.
One of the "benefits" of digital technology is the ability to compensate for uncorrected optical faults through intelligent in-camera image processing. Common issues like linear distortion, vignetting, chromatic aberration, soft corners, etc, can be automatically corrected by the processing engine. That allows lenses to be smaller and/or cheaper without sacrificing output quality, and can yield output files that need less post-processing.
I think m4/3 implements this today better/further than DSLRs.
I put quotes around "benefits" because, as always, there's some controversy. Some folks don't want their raw files pre-tweaked...
