I have to agree with you on this, nothing drives me more to distraction with modern web design than the tremendous amounts of wastes space on my screen. I do exactly what you do, zoom the page until the content fills the horizontal width of the screen. (Though often as not, I'm zooming in to the content to push sidebar adverts off the side of the screen like with this site http://www.geek.com/). I have a good solid 6-7" of wasted horizontal screen space ignoring the sidebar adverts, 3-4 if I add them.
All that being said, I do find that raw text that spans the screen to be harder to read...mostly because it's easier to get lost ending a line on the far right of my screen and returning to the far left (especially if the font it small, something that zooming the page up doesn't seem to have as much problem with).