When you use a normal map in code those 'few lines' reference multiple functions that can add up to total hundreds of lines in length. Those 'few lines' you're referring to arent really a few lines, believe me...
actually those few lines for normalmap, really are just a few instructions, not sure where your "hundreds of lines" would come from, but for tangent space normalmap you only need to "rotate" your normalvector in the right direction, which is just a handful instructions, as ambershee said.
I think I saw ATI's stuff on this, and some work done along these lines for Milo, looked like it could be quite good. This is very true, and I suspect a megatexture solution for lighting could be a nice tradeoff, maintaining the reuse of high quality textures with streamed, atlased lightmaps.
It really, really isn't ;) Normal mapping is a couple of lines of shader math. Dynamic displacement and tesselation is a whole different kettle of beans. In either case, I fully expect the next generation of games (and current PC games) to make use of displacement ever increasingly over the next couple of years, alongside…