Well, you have to fit in both the 800px wide (less than that because of a sidebar that contains ads and other doohickeys) screen to accommodate the lowest common resolution for people who have not upgraded to a monitor made after 2000, and you want most of your content to appear above the fold (less than that with a monstrous header image). Plus, who's looking at the code? The prose is where the actual content is at, right?
The worst part of this is that these kinds of themes make it really hard to change a few things quickly in the CSS (which I use firebug for occasionally) to make it easier to read. I've started skipping things that have layouts that make me work to read 'em. At least all the people who are not techy using low resolutions can read your tech blog post.