One tip, make sure that your designs also fit the screen widths on larger monitors as well. Now number four. From a purely designer oriented viewpoint, yes it should be first. But, if you do not design for the first three principles, the chances of anyone seeing those very creative, awesome graphics is minimal. Another consideration when designing in a commercial environment is money.
Lets face it, website design is about putting money in pockets.
If you are putting more money in the pocket you are going to get a better website. That is nothing more than real world economics influencing design. It would be great to spend hours designing the perfect image, but sometimes an equally attractive but less detailed image must be designed. That is not to say that an inexpensive website should look cheap. In fact the opposite is true.