Brett, as far as I know you are right. Strict HTML 4 does not include margin attributes, they are CSS and IE extensions.
Here's the best cross-browser information I could gather about page margins. Thanks to Lisa Schmeiser at macworld [macworld.zdnet.com] for the bulk of this information.
The amount of extra space a browser adds to your layout depends on the user's platform: on the Mac, whether you're viewing a page with Navigator or Internet Explorer, the layout will move 8 pixels down and 8 pixels to the right. PC users have it even worse: the offset in Internet Explorer for the PC is 10 pixels down and 15 to the right.
The solution? Add margin attributes to your ‹body› tag. You need four of them.
1) marginwidth determines how many pixels of space are between the left edge of a browser window and the items within an HTML document's body.
2) marginheight sets the placement of items relative to the top of the browser.
3) leftmargin tells the browser the pixel width of the left margin (similar to the marginwidth attribute).
4) topmargin tells the browser the pixel width of the top margin (similar to the marginheight attribute).
Even though there seems to be duplication here, you need all four because Internet Explorer 3.0 supports the marginwidth and marginheight tags while the 4.0 browsers support the leftmargin and topmargin tags. Unfortunately, if your users access your site with Navigator 3.0, you're out of luck -– there's no way to get rid of the margin offset with that browser.
As noted above in this thread, even if you are using all four attributes, Netscape will add a 1 pixel margin, and there is no known workaround.
If your design allows, you can declare a background hex color that makes this little sliver less obvious, but that's as far as it goes -- and with a background color defined you must then consider how to define the background for the main area of your page so that readability isn't compromised.