Most digital cameras have a fixed zoom lens that can't be removed or replaced. One big advantage is that the camera is sealed so no dust can get on the image sensor. Digital SLR cameras have removable lenses so you can change them when circumstances dictate.
Infrared photography allows us to see the world in a way that our naked eyes (and traditional cameras) can not. The infrared spectrum exists beyond the spectrum of visible light, but it is always present and can have a very dramatic effect on your images when properly captured.