1) In the real world, you compete for the woman's attention only with people she sees throughout her day. Out of which maybe 5 will initiate a conversation.
On the net, same woman, you are competing with every single guy within 50 miles. Out of which almost every single one will initiate a conversation.
2) In the real world, you see the woman as she is.
On the web, you see myspace angles, copy pastes of likes/dislikes. And lets not forget all those bots and guys pretending to be a girl .
3) You gotta remember that if a woman is good looking, there is ABSOLUTELY no reason for her to go on a crappy dating site. Its not like she doesn't get offered dates everywhere she goes.
Same goes for the guys really, you'll have much higher chances if you start asking women in the real world.