If you are downmodding this, quickly read some craigslist person seeking person posts.
I would guess the majority are just looking for random sexual hookups. Some sort of eHarmony matching for sexual partners would probably be an overwhelming success.
Strangely enough, I know someone who got a PhD studying behavior on dating sites. She worked with a few dating sites and had access to their data. She also came up with clever ways to mine data from sites that didn't give her explicit permission. You're right in doubting the 10:1 ratio - it is more like 20:1 to 100:1 depending on what site you're on.
I don't disagree with you or your friend's numbers.
What I was trying to say was the number of women in general who participate in something like one night stands or a purely sexual relationship MUST be closer to 1:1 than 10:1 or 100:1.
Hence, there is great opportunity in putting together both sides of the equation, online sites by your numbers need to somehow draw the attention of women who they are clearly neglecting to serve well.
getting laid with online dating ?