Decimation master is very smart about what gets culled out of the mesh, their algorithm works really hard to preserve detail. It isn't some brute force poly cruncher, just welding whatever in near, it's very intelligent. Normally what gets hacked out is nothing but fluff that isn't actually contributing to the tiny details…
I don't wanna sound rude, but I find that hard to believe. I think the normal map of the sculpted detail of the x mio. mesh would look different, then the normal map of the same sculpt decimated to few hundred k. Wouldn't it? Enlighten me please :D EDIT: Okay, sorry if I DID sounded rude. I just tested a decimation to 10%…