p.hawksIt does a good job at photo and video. It is full frame, has a very good AF system, and is half the price of a 1D X. For video, it features a number of high bitrate options, as well as being able to shoot raw with magic lantern (at 1080p). It is good at photo and video individually, but doing both well for the price makes it a great deal. Also, many people who started out with t2i's invested in canon glass over the years. They likely have a number of lenses they like, all of which (excluding ef-s) will work on the 5d3. There may be a few things I'm missing, but that is the main idea of it.
Thanks for the clarification!