The problem is that your "object code" is someone else's "source code". When you follow standards, it's easy for people to use what you've published; when you don't, it's painful.

A simplistic example: say you put out a typical web page with a navigation area and content area. Maybe for some reason, your website is much easier for me to use if I put the navigation above or below the content or maybe you put it on the left, and it works better for me on the right. If you used standard practices (CSS) to position your elements on the page, it's really easy for me to go in and mold that to exactly what I want. Why? Because it's the standard, so there are plenty of tools out there for this. All I do is tell the browser to overlay my css rule on your page and I'm done. On the other hand, if your layout is done with tables, well then it becomes much more difficult because you didn't follow the rules that the majority of us have agreed to.