Think about it. When was the last time you actually read a website copy that extends for more than 500 words? One that you really read from the first sentence to the last? I bet you can't remember and it's just normal because seldom do people read much online today.
People usually skim or scan a web page. They don't really make any full reading because, well let's accept it, since the web is very dynamic, people's attention span is very short. They know that they don't have to waste their time on a useless page if they can also easily find a better article on other sites.
So in my opinion, short and concise copy is the best copy for any website. Unless of course it's fiction, it is understood that you need more than 500 words. But if what you have is a blog or a product review site, it will be for your benefit to limit your copy's words to less than 500 words.
I believe I've read in a usability study before that the best word count should be 150 words. If you make it up to 300 words, that's still okay, just stay away from 500 up to a thousand.