Working on the current selection makes a lot of sense, especially if you have a massive model and you only want to work on part of it. If the whole lot was displayed, it would be a visual mess and very difficult to pick out particular parts to work on.
The ability to control individual texture coordinates is one of the reasons why AC3D's UV mapping is popular.
Here's a video of someone making a treasure chest and creating a UV map:
https://www.youtube.com/watch?v=NNh81S__vNo
(the AC3D UI is slightly older but it works much the same way)