Right. Mipmapping is different than simply using lower levels of detail textures. Mipmapping is when you store the full level of detail plus progressively lower levels of detail (always adding up to 33% more data) so that the correct LOD texel can be looked up depending on the required rendering detail. You're using more memory for higher quality (and sometimes faster) rendering.
What is it when you have the detail texture loaded in such a way that you can say "get every second byte (or whatever)" to get the half size, and so on?
IIRC some CPUs were good at that kind of memory access, but most were not.
