Just perusing the Nexus (feel free to point out any link errors, some of these are hosted atypically)....
HG Eyecandy Body 1.3M dl, 332k un
I wouldn't include Ren's or similar cosmetic mods in the nvde mod category, personally, but YMMV.
Number of Dloads (non-unique) from several sites:
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OOO: 189K PES
OOO: 378K gamefront (should include tesnexus numbers)
MMM: 178K PES
Fran's: 297K PES
OWC: 106K www.worldofelderscrolls.de
For OOO & MMM @ PES, I summed the different download options because they're "competing" alternatives, and I assumed it's rare for someone to download a 400MB .7z and then re-download it as an exe.
I'd bet that there's greater spread of downloads for these mods (they're big, and a lot of official links go to megaupload, 4shared, etc), but there's also a lot of "shared" downloads (I use all 4 mods above).
Anyway, as you said, the data is hard to interpret. I don't think the Nexus numbers show an accurate picture of these mods for Oblivion--I don't know of any popular FO alternatives, but I think you're right and I misjudged the numbers.
(Great, another blow to my faith in humanity. thanks.)