All websites are different and they are differently designed. In some cases, however, the background of the website can play a key role in the design. We recently revamped our site dulcetsolutions.com. Now it is based on the html 5 boilerplate. But more importantly, it looks spectacular. And that is largely due the background images that have been put in place. Remove them, and see what you are left with.
Now See the same thing without the background photo.
I wont spit on it. However, that said, if you use pretty much any dark background on this site, it will look pretty decent if not quite as spectacular as the first one.
The single biggest advantage with the first background is that it gives you a LOT of flexibility in terms of color combinations. You can have a red logo, pink logo or even blue logo and it will look good EVERY TIME.