Doom 3 has real-time light preview... I don't want that. When I said light-preview I meant something more like UnrealEd where you hit a light-compile button (and you can adjust settings) and see the changes. Compiling light in hl2 is so much faster than hl1 thanks to all point based lights adding a features like this would be pretty easy.
As for you RAM problem with steam, and working with hammer through steam does blow ass, what I do is quit the editor/steam and compile with bat files to make it that much faster.
Yes they can get away with it, and have, and will but that doesn't mean it shouldn't have been done. Maybe hl2 wouldn't have taken 5 years. D: