Applies to all lenses.
Because it's a function of the camera, not a fancy feature of the lens.
It's because the CMOS image sensor in the back of the digital camera is smaller than the frame of a 35mm film.
Think of it, if you like, as taking a 35mm shot, printing it, then cutting a strip off all four edges of the print, then blowing what's left up as your final print. Or a permanent "zoomed in a bit more" factor.
Whatever lens you use, only that middle rectangle of the "Normal" image ends up captured by the CMOS.
Sensors get bigger - there are already D-SLRs with "full size" sensors (e.g. same size as a 35mm film frame) so the lens "factor" for those is 1:1.