Why? It isn’t necessary. All you end up doing is adding unnecessary extra CSS and in some cases having to add an extra div to your HTML as a page wrap. Not all layouts require a separate wrapper div in addition to the body element.
Using text-align:center; to force a web page to centre is a hack in my view and certainly not necessary for IE6 or later. For eariler IE’s (for anyone suicidal enough to still build for them) then indeed you’ll use the text-align:center; hack to centre your site via a conditional stylesheet. But really, anyone still using IE5.5 or earlier to browse the web will be well used to broken web sites ;) and the worst that would happen in those very old browsers is that the site will be left aligned, so still otherwise fully functional.