Why most Web pages are formatted in portrait orientation? Last time I checked most PC monitors were 4:3 wide. Browsing gets even worse with new 16:9 displays. Some sites do resize with the browser window, but good chunk of them doesn't. I guess one might say 'what if user wants to print it'? I don't honestly know how often typical Web user prints pages, but I personally do it very infrequently compared to how many pages I read.
Is there a reason or is it simply a tradition?