Everyone's personal biochemistry is different. The odour doesn't come from the sweat itself, but from the microorganisms that live in it. What you smell is essentially bacteria ****. Regular perspiration doesn't have that problem, since it's fairly pure water with electrolytes, salts, etc.. Sweat glands in the armpits, groin, and nipples, however, also release an oily substance that bacteria love to nibble on. I'm afraid that I can't remember any specifics right now, but Moonbear and a few other high-mojo biologists will be able to give you more info.
edit: **** meant feces. I just call it like I see it and rely upon the censor software to rein me in.