Well, that did the trick. Here's the code that was making the difference - <div id="main_image">, which is another container that all the other pages have, but the index doesn't. Here is the css for the main image div:
The funny thing is it doesn't even need the </div> to solve the problem - with just the opening the logo in the banner div shifts over. I closed the tag to have cleaner code, and of course deleted all the main image content and there you go. If anyone can see why that main image div would be shifting the content of the banner div, I'd love to have that little bit of knowledge for the next time something like this happens. Thanks!