The 18 is a true 18 on that 18-135 because the lens is designed for the crop sensor (ef-s).
So if you have a 100mm lens, it will give you a certain field of view on a 35mm SLR (or full frame digital). If you use that same lens on a 'crop body', the focal length is still 100mm....but the outsides of the image circle (projected by the lens into the camera) will not be recorded by the camera's sensor (because it's smaller). So you end up with an image that covers a smaller field of view.
It doesn't matter if the lens is EF or EF-S....50mm will give you the same FOV (on the same camera).
The only reason why the crop factor exists, is because the 'standard' for so long was 35mm film. So when they came out with cameras of the same size & format, but with smaller sensors...they wanted to let people know that the FOV would be different that what they were used to with 35mm film.