Why do so many "professional" sites display in fixed 800px width, including this

I'm going to guess you are a designer like me who encourages "fluid" or "liquid" displays that use all of the screen's real estate. I worked on a fluid site for a number of years and realized that sometimes my design might look a little different than I intended it at certain browser sizes. It is also sometimes difficult to get items to layout properly. However, to me the benefits of allowing the user to adjust the screen width outweighed my dislike for how the page might look at some sizes. Most of Yahoo! uses a fixed screen size. This is probably due to a graphic designer being in charge of the spec guidelines. They probably want everything to be pixel perfect and can't stand the thought of the possiblity of something being out of line. Designers need to realize that many users have multiple browsers open at once. If the web sites aren't fluid, then browsing the two sites at once will require using the horizontal scroll bar that nobody likes to use. I like everything about this site except it rigid width design.