980 is not the "defacto standard", you'll generally see most people targeting a size a little bit less than 1024px wide to account for browser chrome such as scrollbars, etc.
Usually people target between 960 and 990px wide. Often people use a grid system (like 960.gs) which is opinionated about what the default width should be.
Also note, just recently the most common screen size now averages quite a bit bigger than 1024px wide, ranking in at 1366px wide. See http://techcrunch.com/2012/04/11/move-over-1024x768-the-most-popular-screen-resolution-on-the-web-is-now-1366x768/