Cropping is the same as getting closer. Cropping, in this sense, is about cropping an image when processing, but it also refers to standing in one place and zooming in and out. When you set up your camera in one spot and zoom, you're essentially cropping your scene. To prove it, try taking some photos from one spot with your camera on a tripod and shoot a wide shot and then a telephoto shot. In the computer, crop your wide to match the composition of your telephoto shot, and you can see that it matches exactly, other than possibly losing some image quality due to the crop.
Physically moving closer to or farther from your subject changes things that can't be changed by cropping or zooming. As you move, you change relationships of foreground to background, you alter perspective, and you affect the appearance of space within your photograph. These things can be significant, which is why the same subject shot with a wide-angle lens up close and with a telephoto lens from farther away will have totally different looks even if the subject is the same size in both photos.