It's most definitely not luck, though of course that always plays a part. I can tell you straight up the guys here who will never have their ads or PMs or IMs answered:
Those who constantly talk about their 'standards', which even the most beautiful girls here would feel that they couldn't live up to.
The guys that are mean-spirited in their posts-fellas, girls do look to see what you've written besides your ad.
The guys that seem to have zero personality and don't care if we have one, all they want is a body to tickle. Not appealing, sorry.
And the whiners who are always saying how they can't find anybody here and no one ever talks to them. We assume their must be a reason, wouldn't you?
DVNC is absolutely right, it's how you present yourself.
Though being a crazy white boy can help...
Bella