I see you don't understand how source/gs works.
Since they are not realtime engines everything has to be precomputed for them (lightmaps, geometry etc...) hence why we compile.
It would be impractical to have an ingame editor, if your pc is slow running the game at the same time would not be the best mapping experience, having to alt+tab every time you need to edit a model, sound, texture would be a pain and would kill productivity.
Doom3 and Quake4 had a built in editor, even though they used dmap(not sure exactly) some elements still had to be compiled.
There is an ingame editor for Portal 2, but is very primitive though interactive
I agree hammer is a bit "out of date" compared to other editors, but we got used to it, and so will you.
Btw you can't link images from you pc, upload them to the web first (imgur, imageshack ...)