I believe WP leaves the original image intact but it does create several different sized images, how many and what sizes really depends on the theme and the plugins you have installed. When WP or plugins need a specific image size it uses that cached image.
Connections is wired a bit differently. Rather than trying to create n-number of images right off the bat, it creates them on demand and then caches them for future use. When Connections create these alternative sizes it uses the original image. Really the process is the same, just happens at different point in time.
Hope that helps!