Not everyone loves clubbing. Sure, the thumping music and expensive cocktails can be fun sometimes, but as a way to meet a new boyfriend or girlfriend the club scene leaves a lot to be desired. First off, it's dark in there, so a person that looks luscious in their makeup and best going-out clothes may not look so gorgeous in broad daylight. Dating someone you met in the dark can be a rude shock.
Secondly, night clubs are by nature loud. They're great places for dancing but not so great for conversation, and while dating someone with fantastic moves is good fun, it'll soon wear thin if you don't have more in common than that. Sooner or later you'll want to do more than just dance.
Dating websites are completely different. Online you usually get to see at least one or two pictures, so you have a fair idea what the guy or girl actually looks like in a good light, and it's all about conversation. Whether you chat or exchange messages, it's easy to get an idea about whether or not you have a similar attitude and enjoy similar things.
There is one other advantage dating websites have over clubs: it's very clear what a potential date's intentions are. In a club, it's hard to figure out whether they're just flirting, have a girlfriend or a boyfriend already, and even whether they're gay or straight. Online, all the information you need is there up front. It saves a lot of time and quite a bit of needless embarrassment.